HX64089339 
QP34  .R21  A  manual  of  human  ph 


RECAP 


Columtiia  ®nibersiitp 
intfieCitpofi^clogorfe 

COLLEGE  OF  PHYSICIANS 
AND   SURGEONS 


Reference  Library- 
Given  by 


Frederic  S.  Lee, 

Columbia  College, 
New  York- 


PLATE    I. 


A,  upper  bone  of  sternum  ;  B,  B,  two  first  ribs:  C,  C,  second  pair  of  ribs  ;  D.D,  right 
and  left  lungs;  E,  lower  end  of  sternum  :  F  F,  right  and  left  halves  of  the 
diaphragm  in  sections  :  the  right  half  separating  the  right  lung  from  the  liver, 
the  left  half  separating  the  left  lung  from  the  broad  cardiac  end  of  the  stomach; 
G,  G,  eighth  pair  of  ribs;   K,  K,  ninth  pair  of  ribs. 


Sauntiets'  Mcio  SiS  Stties 


A    MANUAL   OF 
HUMAN 

PHYSIOLOGY 

PREPARED   WITH    SPECIAL   REFERENCE   TO 

STUDENTS   OF   MEDICINE 


BY 

JOSEPH  H.  RAYMOND,  A.M.,  M.D., 

PROFESSOR   OF    PHYSIOLOGY   AND    HYGIENE   IN   THE   LONG   ISLAND   COLLEGE    HOSPITAL, 
AND    DIRECTOR   OF   PHYSIOLOGY   IN  THE   HOAGLAND    LABORATORY. 


WITH   102    ILLUSTRATIONS   IN    TEXT   AND 
4  FULL-PAGE   COLORED    PLATES. 


PHILADELPHIA 
W.    B.    SAUNDERS 

925  Walnut   Street. 
1894. 


B^fJ^lGAWIjaRAKi 


Copyright,  1894,  by 
W.    B.    SAUNDERS. 


ELEOTROTYPED    BY  PRESS    OF 

WESTOOTT  8.  THOMSON,   PHILADA.  W.   B.   SAUNDERS.   PHILADA. 


PREFACE 


The  author's  experience  of  twenty  years  as  a  teacher 
of  Physiology  to  medical  students  has  brought  him  to 
the  conclusion  that  in  the  short  time  allotted  to  the 
study  of  physiology  in  medical  schools  students  can 
assimilate  only  the  main  facts  and  principles  of  this 
branch  of  medicine,  which  lies  at  the  very  foundation 
of  a  sound  knowledge  of  the  healing  art;  and  that 
even  if  there  were  time  to  investigate  the  more 
recondite  and  abstruse  parts  of  the  subject,  such  an 
investigation  would  be  profitless  during  this  formative 
period.  In  his  teaching  the  author  has  kept  this 
thought  constantly  in  mind,  and  in  this  manual  has 
endeavored  to  put  into  a  concrete  and  available  form 
the  results  of  his  experience. 

SEPTKMnKR,    1894. 


Digitized  by  the  Internet  Archive 

in  2010  with  funding  from 
Columbia  University  Libraries 


http://www.archive.org/details/manualofhumanphyOOraym 


CONTENTS. 


PAGE 

Introduction 17 

I.  Physiologicai,  Chemistry 25 

Inorganic  Ingredients,  27 ;   Carbohydrates,  41  ;   Fats  and  Allied 
Substances,  53;  Proteids,  57;  Food,  82. 

II.  NuTRiTivK  Functions 92 

1.  Digestion,  92:   (A)  Mouth,  95;   (B)  Stomach,    103;   (C)   Intes- 

tinal,  118. 

2.  Absorption,  131  :   Structure   of  Villi,  131  ;   Lymph,  133;  Chyle, 

134;  Absorption  of  Fats,  135.  Blood,  136:  Physical  Proper- 
ties, 136;  Color,  137;  Reaction,  137;  Odor,  137;  Taste,  137; 
Quantity,  137;  Distribution,  137;  Temperature,  138;  Micro- 
scopical Structure,  138;  Red  Corpuscles,  138;  Number  of 
Corpuscles,  139;  Color  of  Red  Corpuscles,  139;  Structure  of 
Red  Corpuscles,  139;  Development  of  Red  Corpuscles,  140; 
Destruction  of  Red  Corpuscles,  140;  Function  of  Red  Cor- 
puscles, 140;  White  Blood  Corpuscles,  141  ;  Composition  of 
White  Corpuscles,  142;  F'unclion  of  White  Corpuscles,  142; 
Plaques,  142;  Composition  of  Plasma,  143;  Coagulation,  143; 
Causes  of  Coagulation,  145  ;  Gases  in  the  Blood,  147. 

3.  Respiration,  149:  The  Nose,  149;   Mouth  Breathing,  150;  The 

Trachea,  151 ;  The  Bronchii,  152;  The  Lungs,  152;  The 
Thorax,  153;  Inspiratory  Movements,  154;  Expiratory  Move- 
ments, 155  ;  Movements  of  Glottis,  156 ;  Capacity  of  the  Lungs, 
'57;  Vital  Capacity,  158;  Frequency  of  Respiration,  158; 
Cause  of  Resjiiration,  158  ;  Types  of  Respiration,  158;  Chem- 
istry of  Respiration,  159;  Expired  Air,  160 ;  Ventilation,  161; 
Changes  in  the  Blood  due  to  Respiration,  163 ;  Internal 
Respiration,  163. 

7 


CONTENTS. 

4.  Vital  Heat,  164:   Warm-blooded  Animals,  165;   Homoiothermal 

Animals,  165;  Poikilothermal  Animals,  165;  Heat-unit,  166; 
■  Sources  of  Heat,  166 ;  Temperature  of  Different  Parts  of  P>ody, 
167;  Temperature  at  Different  Ages,  167;  Daily  Variations  in 
Temperature,  168;  Instances  of  High  and  Low  Temperature, 
168;   Regulation  of  Temperature,  169. 

5.  Circulation  of  the  Blood,  170:   The  Heart,  170;   Right  Auricle, 

1 70;  Right  Ventricle,  170;  Left  Auricle,  171  ;  Left  Ventricle, 
172;  Cardiac  Valves,  172;  Pulmonary  Valves,  173;  Mitral 
Valve,  173;  Aortic  Valve,  174;  The  Arteries,  174;  The  Ca- 
pillaries, 174;  The  Veins,  175  ;  Circulation  of  the  Blood,  175  ; 
Cardiac  Movements,  176;  Movements  of  Blood  during  Systole 
and  Diastole,  177;  Shortening  of  the  Heart,  180 ;  Cardiac 
Impulse,  180;  Papillary  Muscles,  181 ;  Cardiac  Sounds,  1S2; 
Characteristics  of  Cardiac  Sounds,  182;  Causes  of  Cardiac 
Sounds,  182;  Circulation  in  the  Arteries,  183;  Internal  Fric- 
tion, 184;  Arterial  Pressure,  185  ;  Rate  of  Flow  in  Veins,  185  ; 
Pulse- wave,  186;  Circulation  in  the  Capillaries,  187;  Circula- 
tion in  the  Veins,  187  ;  Compression  of  the  Veins,  188;  Aspira- 
tion of  the  Thorax,  188;   Force  of  Gravity,  188. 

6.  Lymphatic  System,   189:    Lymphatic  Vessels,    189;    Lymphatic 

Glands,  190. 

7.  Ductless    Gla7ids,    191  :     The    Spleen,    192;    Functions    of  the 

Spleen,  192;  Thymus  Gland,  193;  Thyroid  Gland,  194;  Su- 
prarenal Capsules,  194;    Pituitary  Body,  194. 

8.  The    Skin,   195:    Corium,   195;    Epidermis,    196;    Perspiratory 

Gland,  196;  Office  of  Perspiration,  199;  Sebaceous  Gland,  199; 
Composition  of  Sebum,  200;  Cerumen,  200;  Hairs  and  Nails, 
200  ;  Functions  of  Skin,  200  ;  Protection,  201  ;  Excretion,  201  ; 
Sensation,  202  ;  Respiration,  203  ;  Regulation  of  Temperature, 
203  ;  Care  of  the  Skin,  203  ;   Baths,  204. 

9.  The  Kidtieys,  204  :  Urine,  207  ;  Water,  209  ;   Urea,  209 ;   Source 

of  Urea,  209;  From  Proteids  of  Food,  209;  From  Proteids 
of  Tissue,  210;  From  Proteids  of  Blood  and  Lymph,  210; 
Uric  acid,  211  ;  Source  of  Uric  Acid,  212;  Hippuric  Acid, 
212;  Creatinin,  212;  Inorganic  Constituents  of  Urine,  212; 
Coloring-matter  of  Urine,  214;  Mucus  of  Urine,  214;  Gases 
of  Urine,  214. 


PAGE 


CONTENTS.  9 

PAGE 

III.  Nekvous  Functions ^'5 

General  Considerations,  215.     Termination  of  Ne,-ve-fibres,  220 : 
Corpuscles  of  Tacini,  221  ;  Tactile  Corpuscles,  221  ;  End-bulbs, 
221.    Chemistry  of  Nervous  Matter,  22\.    Fjtndions  of  Ne)-ve- 
celis  and  Nerve-fibres,  221.      Classification    of  Nerve-centres, 
221:  Conscious,  222;    Reflex,  222;   Automatic,  222;    Relay, 
222;    Junction,    222.       Classification     of   Nerve-fibres,     222. 
Efferent  Nerves,  223:   Motor,  224;   Vaso-motor,  224;   Secre- 
tory, 224;  Trophic,  224;   Inhibitory,  224.     Afferent  Ne>-ves, 
224 :   Sensory,  225 ;   Nerves  of  Special  Sense,  225  ;  Thermic, 
225  ;  Excito-r'eflex,  225  ;  Inhibitory,  225.     Intcrccntral  Nerves, 
225.'    Nen'estimuli,  226:  Classification,  227;  General,  227; 
Special,  227.      General  Arrangement  of  Nervous  System,  227  : 
Certhro-spinal  System,  22T.    Spinal  Cord,  228;   Enlargement, 
228;  Fissures,  228;  Section  of  Spinal  Cord,  230;  Minute  Struc- 
ture,'230;  Tracts  in  the  Cord,  231  ;  Gray  Matter,  232;   Nerves, 
233;    Functions  of  Nerves,  233;  Recurrent  Sensibility,  233; 
Ganglia,  234 ;  Connection  of  Nerve-roots  with  the  Cord,  234 ; 
Conductor  of  Impulses,  235  ;   Methods  of  Examination,  235  ; 
Conducting-paths,    236;    Nerve-centres,  237;    Reflex    Action, 
237.     Special  Centres,  240 :  Musculo-tonic,  240;  Respiratory, 
240 ;  Cardio-accelerator,  241 ;  Vasomotor,  241 ;  Sudorific,  24I  ; 
Cilio-spinal,  241  ;  Genilo-spinal,  241 ;  Ano-spinal,  241 ;  Vesico- 
spinal, 243;  Trophic,  245;  Various,  245. 

The  Brain,  246:  Weight,  246;  Gray  Matter,  246;  White  Matter, 
246.  Medulla  Oblongata,  247:  Fissures,  248;  Funiculi,  248; 
Functions,  249;  Nerve-centres,  249;  Reflex  Centres,  249; 
Control  on  Deglutition,  249;  Control  on  Vomiting,  249;  Cen- 
tral Vomiting,  250;  Rumination,  250;  Automatic  Centres,  250; 
Respiratory  Centre,  251;  Resistance  Theory  of  Respiration, 
251;  Asphyxia,  252;  (l)  Dyspnrea,  253;  (2)  Convulsion,  253; 
(3)  Exhaustion,  253;  (4)  Inspiratory  Spasm,  253;  Cardio-inhib- 
itory  Centre,  254;  Vasomotor  Centre,  254;  Depressor  Nerve- 
fibres,  255.  Pons  Varolii, 21^:  Functions,  256.  CerebellufU, 2^6: 
Functions,  257.  Cerebrum,  258.  Fissures,  259  :  Fissure  of 
Sylvius,  260;  Fissure  of  Rolando,  261 ;  Parieto-occiiiital  Fis- 
sure, 261.  Lobes  of  Cerebrum,  262:  Frontal  Lobe,  262  ;  Pa- 
rietal Lobe,  263;  Occipital  Lobe,  263;  Temiwro-sphenoiflal 
Lobe,  263;  Central  I-obe  on  Island  of  Reil,  263.  Crura 
Cerebri,  263.   Basal  Ganglia,  264 :  Corpora  Striata,  264;  Optic 


lO  CONTENTS. 

PAGE 

Tlialami,  264;  Tubercula,  or  Corpora  Quadrigemina,  264.  Mi- 
croscopical Structure  of  Hemispheres,  265:  Gray  Matter,  265; 
White  Matter,  2^"].  Functions  of  the  Cerebrtcm,  268;  Mem- 
ory, 270;  Reason,  270;  Judgment,  270.  Cerebral  Localization, 
271  :  Centre  for  Motion,  272;  Centre  for  Speech,  273;  Sen- 
sory Areas,  273 ;  Auditory  Centre,  274 ;  Optic  Centre,  274 ; 
Olfactory  Centre,  274 ;  Functions  of  Corpora  Quadrigemina, 
274;  Functions  of  Corpora  Striata  and  Optic  Thaiami,  274. 
Cranial  Nerves,  275  :  Olfactory  Nerve,  276 ;  Optic  nerve, 
277;  Motor-oculi  Nerve,  278;  Trigeminus  Nerve,  281;  Ab- 
ducens  Nerve,  289 ;  Facial  Nerve,  290 ;  Auditory  Nerve,  292 ; 
Glosso-pharyngeal  Nerve,  293 ;  Pneumogastric  Nerve,  293 ; 
Spinal  Accessory  Nerve,  297 ;  Hypoglossal  Nerve,  298. 
The  Senses,  299 :  General  Sensibility,  299 ;  Sense  of  Tojich, 
299 ;  Sense  of  Pressure,  300 ;  Sense  of  Temperature,  300 ; 
Sense  of  Pain,  300;  Sense  of  Smell,  301 ;  Sense  of  Taste,  303  : 
Conditions  of  Sense  of  Taste,  305 ;  Sense  of  Sight,  306 :  Sclerotic 
Coat  of  Eye,  306 ;  Cornea,  307 ;  Choroid,  307 ;  Iris,  307  ;  Cil- 
iary Muscle,  308;  Retina,  309;  Layers  of  Retina,  309;  An- 
terior and  Posterior  Chambers  of  Eye,  310;  Vitreous  Body, 
311 ;  Crystalline  Lens,  311;  Suspensory  Ligament,  312;  Ar- 
terial Supply  of  Eye,  312;  Physiology  of  Vision,  312;  Accom- 
modation, 315  ;  Phakoscope  of  Helmholtz,  317  ;  Emmetropia, 
318;  Ametropia,  318;  Myopia,  318;  Hypermetropia,  319; 
Presbyopia,  319;  Astigmatism,  319;  Functions  of  Retina, 
319;  Movements  of  Eyeball,  321 ;  Appendages  of  Eye,  321 ; 
Lachrymal  Apparatus,  321 ;  Meibomian  Glands,  323.  Sense 
of  Hearing,  323:  External  Ear,  323;  Middle  Ear,  324;  In- 
ternal Ear,  325;  Vestibule,  326;  Semicircular  Canals,  326, 
328;  Cochlea,  326;  Organ  of  Corti,  327;  Mechanism  of 
Hearing,  328;  Eustachian  Tube,  331.  Sympathetic  Nervous 
System,  331 :  Sympathetic  Ganglia  and  Nerves,  333;  Functions 
of  the  Sympathetic,  334. 

IV.  The  Reproductive  Functions 336 

Reproductive  Organs,  336.  Genital  Oigans  of  Male,  336  :  Testes, 
336;  Spermatozoa,  336;  Vas  Deferens  and  Vesicula  Seminalis, 
339.  Genital  Organs  of  Female,  339  :  Ovary,  339;  Parovarium, 
342 ;  Ovum,  342 ;  Fallopian  Tubes,  343 ;  Uterus,  345.  Ovulation, 
345  ;  Menstruation,  347 :  Composition  of  Menses,  348 ;  Cause 


CONTENTS.  II 

of  Menstruation,  349;  Relation  between  Menstruation  and 
Ovulation,  350;  Formation  ol"  Corpus  Luteum,  351 ;  Matura- 
tion of  the  Ovum,  351  ;  Method  of  Fertilization,  354;  Mem- 
branes of  the  Embryo,  358;  Amnion,  358;  Yolk-sac,  359; 
Allantois,  359;  Chorion,  360;  Placenta,  360.  Circulation  in  the 
Embryo,  362  :  Vitelline  Circulation,  362 ;  Placental  or  Foetal 
Circulation,  362;   Changes  in  the  Circulation  at  Birth,  365. 


LIST  OF  ILLUSTRATIONS. 


FIG.  PAGE 

1.  Partial  or  Green-stick  Fracture 38 

2.  Bone  Tied  in  Knot 39 

3.  Starch-grains 43 

4.  Diagram  showing  Proportion  of  P^ood-stufis 86 

5.  Stomach  and  AHmentary  Canal 93 

6.  Salivary  Glands 98 

7.  Muscular  Coat  of  Pharynx  and  (Esophagus loi 

8.  Cardiac  Glands 105 

9.  Left  Breast   and   Side,  sliowing  perA^ratioii  of  walls  of   stomach 

of  Alexis  St.  Martin io6 

10.  Portion  of  Wall  of  Stomach,  showing  valvula.' conniventes    ...  119 

11.  Vertical  Section  of  Duodenum 120 

12.  Section  of  L<jl)ule  of  Rabbit's  Liver 122 

13.  The  Liver 123 

14.  Section  of  Liver  of  Newt 124 

15.  Microscopical  Constituents  of  Stools 130 

16.  Monads  from  Faces 130 

17.  Villus,  with  capillaries  injected 132 

18.  Diagram  showing  Course  of  Main  Truid<s  of  Absorbent  System    .  133 

19.  Blo(jd-corpuscles  (Eljerth  and  Schininiclbusch) 139 

20.  Changes  in  Leucocytes  of  Frog  {Am.   Text-book  0/  Surgery)  .    .  142 

21.  Organs  of  Respiration    .    .             i:;! 

22.  Skeleton  of  Thorax 152 

23.  Interior  View  of  Diaphragm 153 

24.  Larynx  in  Gentle  Breathing 156 

25.  Larynx  in  Deep  Breathing 156 

26.  Interior  (jf  Right  Auricle  and  Ventricle 171 

27.  I,eft  Auricle  and  Ventricle 172 

28.  Orifices  of  the  Heart 173 


14  LIST   OF  ILLUSTRATIONS. 

FIG.  PAGE 

29.  Normal  Vessels  and  Blood-stream 186 

30.  Diagram  of  a  Lymphatic  Gland 190 

31.  Vertical  Section  of  Skin  (diagrammatic) 195 

32.  Section  of  Skin  showing  Layers 1 96 

33.  Section  of  Skin  (Ranvier) 197 

34.  Normal  Sweat-gland,  highly  magnified  (Neumann) 198 

35.  Normal  Sebaceous  Gland  with  Lanugo  Hair  (Neumann)  ....  199 

36.  Section  of  Hair  (Duhring) 201 

37.  Section  of  Skin  (Biesiadecki) 202 

38.  Longitudinal  Section  through  Kidney  (Tyson  and  Henle)    .    .    .  205 

39.  Diagram  of  Two  Uriniferous  Tubules  (Tyson  and  Brunton,  after 

Klein  and  Noble  Smith)   • 206 

40.  Bowman's  Capsule  and  Glomerulus  (Landois) 207 

41.  Uric  Acid  and  Urates  (Funke) 211 

42.  Calcium  Phosphate  (Laache) 213 

43.  Triple  Phosphates  and  Ammonium  Urate  (Laache) 213 

44.  Multipolar  Nerve-cells  (Cadial) 218 

45.  Medullated  and  Non-medullated  Nerve-fibres 219 

46.  Section  of  Injected  Skin  (Cadiat) 220 

47.  End-bulb  from  Human  Conjunctiva  (Longworth) 220 

48.  Difierent  Views  of  Portion  of  Spinal  Cord  from  Cervical  Region 

(Allen  Thomson) 229 

49.  Transverse  Section  of  Half  of  Spinal  Cord  in  the  Lumbar  Enlarge- 

ment (Allen  Thomson) 229 

50.  Diagram  of  Spinal  Cord  at  Lower  Cervical  Region  (Gowers)  .    .  231 

51.  View,  from  below,  of  the  Connection  of  the  Principle  Nerves  with 

the  Brain 247 

52.  View  of  the  Brain  from  above 259 

53.  Outer  Surface  of  Left  Hemisphere 260 

54.  Inner  Surface  of  Right  Hemisphere    .    , 261 

55.  Lateral  View  of  Brain  (combined  from  Ecker) 262 

56.  Motor  Areas  on  the  Outer  Surface  of  Brain 272 

57.  Motor  Areas  on  the  Median  Surface  of  Brain 273 

58.  Base  of  Brain 275 

59.  General  Plan  of  the  Branches  of  the  Fifth  Pair 282 

60.  \ 

r       I  Distribution  of  the  Cutaneous  Sensitive  Nerves  upon  the  Head  .  284 

62.  View  of  the  Nerves  of  the  Eighth  Pair 294 

63.  Nerves  of  the  Outer  Walls  of  the  Nasal  Fossa 301 

64.  Papillar  Surface  of  the  Tongue,  with  the  Fauces  and  Tonsils  .    .  304 


LIST  OF  ILLUSTRATIONS.  1 5 

PIG.  PAGE 

65.  Section  of  Eyeball 307 

66.  Choroid  Membrane  and  Iris,  exposed  by  the  removal  of  the  Scler- 

otic and  Cornea  (Quain) 308 

67.  Diagrammatic  Section  of  Retina  (Schultze) 308 

68.  Fundus  of  an    Eye  containing   little   pigment,  choroidal  vessels 

visible  (Wecker) 31 1 

69.  Normal  Optic  Disk  of  Left  Eye  (Jaeger) .  312 

70.  Principal  Focus  of  a  Convex  Lens 314 

71.  Diagram  showing  Changes  in  Lens  during  Accommodation  .    .    .  315 

72.  Diagram  showing  three  reflections  of  a  Candle 316 

73.  Phakoscope  of  Helmholtz 316 

74.  Movements  of  the  Eyeballs 321 

75.  Muscles  of  the  Eye 322 

76.  Glands  of  the  Eye 322 

77.  Meibomian  Glands 323 

78.  Semi-diagrammatic  Section  through  Right  Ear  (Czermak)     .    .    .  324 

79.  Ossicles  of  the  Right  Ear 324 

So.  View  of  Interior  of  Left  Labyrinth  (Sommering) 325 

81.  Diagram  of  Membranous  Labyrinth  (Gray) 325 

82.  Bony  and  Membranous  Cochlea  laid  open 327 

83.  Section  through  one  of  the  Coils  of  the  Cochlea  (Quain)  ....  327 

84.  Diagrammatic  View  of  the  Sympathetic  Cord  of  the  Right  Side 

(Quain) 332 

85.  Testicle  and  Epididymis  of  Human  Subject  (Kolliker)      ....  337 

86.  Section  of  Tubuli  Seminiferi  of  a  Rat  (Schafer) 337 

87.  Spermatozoa  of  Various  Animals 338 

88.  Posterior  View  of  Fundus  of  Bladder 339 

89.  Section  of  Ovary  of  Cat  (Schron) 340 

90.  Same  as  89,  more  highly  magnified 341 

91.  Posterior  View  of  Left  Uterine  Appendages 342 

92.  Mature  Ovum  of  Rabbit  (Waldeyer) 343 

93.  Fallopian  Tube  laid  open  (Playfair) 343 

94.  Vertical  Section  through    Mucous    Membrane  of   Human  Uterus 

(Turner) 344 

95.  Section  of  Mucous  Membrane  of  Uterus  (ilenle) 345 

96.  Uterus  during  Menstruation  (Courty) 349 

97.  Karyokinesis,  or  indirect  cell  division 352 

98.  Sections  of  Ovum  of  Rabbit  (E.  Van  Beneden) 354 

99.  Diagrammatic  Longitudinal  Section  through  the  Axis  of  an  Em- 

bryo Chick  (Foster  and  Balfour) 358 


1 6  LIST   OF  ILLUSTRATIONS. 


loo.  Diagrammatic  Longitudinal  Section  of  a  Chick  on  the  Fourth 

Day  (Allen  Thomson) 359 

loi.   Diagram  representing  the    Relationship  of   the  Decidua  to  the 

Ovum  at  different  periods  (Dalton) 361 

102.  Diagram  of  Foetal  Circulation         363 


HUMAN  PHYSIOLOGY. 


INTRODUCTION. 

Definitions. — Physiology  is  tJie  science  zvliich  treats 
of  fniictioiis.  By  the  term  "  function  "  is  meant  the 
characteristic  work  performed  by  an  organ.  An  organ 
may  be  defined  as  a  structure  which  performs  a  function. 
Lifeless  things  perform  no  functions,  hence  physiology 
has  no  dealings  with  inanimate  things.  Rocks,  stones, 
and  other  members  of  the  mineral  kingdom  at  no  time 
possess  life ;  consequently  they  perform  no  functions, 
and  with  them  physiology  has  no  concern  :  we  cannot 
speak  of  the  physiology  of  minerals.  Plants  and  ani- 
mals are  sometimes  living  and  sometimes  dead :  when 
living  they  perform  functions,  when  dead  they  perform 
no  functions ;  in  the  latter  condition  they  are  like  the 
rocks  so  far  as  function  is  concerned,  and  with  them 
physiology  has  nothing  whatever  to  do.  It  is  only  when 
they  are  living  that  they  perform  functions,  and  it  is 
then  and  only  then  that  with  them  physiology  concerns 
itself. 

Another  definition  which  might  be  given  of  physiology 
is,  that  it  is  tlie  science  luJiick  treats  of  vital  phenomena. 
A  brief  consideration  of  this  definition  will  bring  us  to 
the  same  conclusion  as  did  that  of  the  above  definition. 
Of  life  in  its  essence  we  know  nothing.  Metaphysicians 
have  endeavored  to  explain  life,  and  some  have  even 
ventured  to  point  out  its  scat,  but  the  fact  remains  that 

2  17 


1 8  HUMAN  PHYSIOLOGY. 

we  are  utterly  ignorant  of  its  nature.  We  only  know 
that  it  exists  by  certain  manifestations  which  it  presents. 
When  we  see  a  growing  plant  or  a  moving  animal,  we 
say  of  each  that  it  is  alive.  In  the  higher  forms  of 
animals  and  plants  it  is  easy,  under  ordinary  circum- 
stances, to  determine  whether  they  are  living  or  not,  but 
in  the  lower  forms  this  determination  is  sometimes  a 
most  difficult  task.  The  evidences  upon  which  reliance 
is  placed  to  determine  the  presence  or  the  absence  of  life 
are  spoken  of  as  "  vital  phenomena."  Thus,  if  in  exam- 
ining an  animal  we  find  that  its  heart  beats,  we  say  that 
the  animal  is  alive,  but  if  the  heart  be  motionless,  we  say 
that  the  animal  is  dead.  This  beating  of  the  heart,  there- 
fore, is  a  vital  phenomenon — that  is,  a  manifestation  of 
life.  We  speak  also  of  this  beating  of  the  heart  as  its 
"  function  "  ;  hence  the  first  definition  of  physiology,  that 
it  is  the  science  which  treats  of  functions,  and  the  second 
definition,  that  it  is  the  science  which  treats  of  vital 
phenomena,  amount  to  the  same  thing. 

"Org-an"  Defined. — Let  us  for  a  moment  consider 
what  is  meant  by  the  term  "  organ."  It  has  already  been 
defined  as  a  structure  which  performs  a  function.  In 
speaking  of  the  organs  of  an  animal  reference  is  usually 
had  to  such  structures  as  the  heart,  the  lungs,  and  the 
stomach,  inasmuch  as  their  size  and  the  important  work 
they  perform  force  them  upon  our  attention.  These  are 
indeed  organs,  for  they  perform  functions  ;  thus  the  func- 
tion of  the  heart  is  to  receive  blood  in  one  portion  and 
to  propel  it  from  another  portion,  that  of  the  lungs  is  to 
aerate  the  blood,  and  that  of  the  stomach  is  to  digest 
certain  kinds  of  food ;  but  the  term  organ,  as  used  in 
physiology,  has  a  much  broader  signification.  A  mus- 
cle, a  nerve,  and  a  blood-vessel  are  as  truly  organs  as 


INTR  OD  UCriON.  1 9 

are  the  greater  ones  above  spoken  of,  for  each  has  its 
own  function.  Thus  the  function  of  a  muscle  is  to  con- 
tract, that  of  a  nerve  is  to  transfer  nervous  impulses,  and 
that  of  a  blood-vessel  is  to  convey  blood.  At  first  sight 
it  might  seem  that  these  functions  were  unimportant, 
and  that  the  structures  which  performed  them  were 
hardly  worthy  of  so  dignified  a  name  as  organs ;  but  a 
moment's  reflection  will  show  that  without  the  contrac- 
tion of  muscles,  the  transference  of  nervous  impulses,  or 
the  carrying  of  blood  the  life  of  an  animal  would  as  cer- 
tainly cease  as  if  it  were  deprived  of  its  heart,  of  its  lungs, 
or  of  its  stomach. 

Inasmuch  as  minerals,  on  the  one  hand,  possess  no 
organs,  they  perform  no  work — that  is,  they  have  no 
functions ;  therefore  we  do  not  speak  of  the  physiology 
of  a  mineral.  Plants  and  animals,  on  the  other  hand, 
possess  organs,  each  of  which  performs  its  special  func- 
tion ;  and  it  is  with  them,  as  has  been  said,  that  physi- 
ology has  to  do.  As  we  find  organs  in  the  animal,  so 
do  we  find  them  in  the  plant ;  not  the  same  organs,  it  is 
true,  but  as  truly  organs,  for  they  respond  to  the  same 
test.  The  roots  of  a  plant  absorb  moisture  and  nourish- 
ment from  the  soil,  this  being  their  function  ;  the  green 
leaves  take  up  from  the  air  carbonic  acid,  with  which 
and  with  water  they  form  starch  that  is  utilized  by  the 
plant,  while  oxygen  is  set  free,  this  being  the  function 
of  the  leaves  ;  the  anthers  and  the  ovaries  of  flowers  are 
concerned  in  reproducing  plants  by  forming  new  ones, 
this  being  their  function.  Thus  we  might  continue  to 
show  that  as  in  animals,  so  in  plants,  the  different  organs 
have  their  respective  functions. 

"  Organic  "  and  "  Inorganic. " — We  can  now  under- 
stand the  meaning  of  two  very  important  terms — organic 


20  HUMAN  PHYSIOLOGY. 

and  inorganic.  These  terms  are  used  in  two  senses : 
first,  as  to  structure,  and,  second,  as  to  product.  When 
we  say  that  a  plant  or  an  animal  is  "  organic,"  we  mean 
that  it  is  made  up  of  organs — that  is,  of  structures  which 
perform  functions.  The  plant  or  the  animal  may  be 
simple  or  may  be  complex,  but,  however  simple  or  how- 
ever complex,  its  parts  do  something,  that  something 
being  the  function  of  the  part  which  acts.  We  say, 
therefore,  that  the  plant  or  animal  is  organic,  meaning 
that  it  is  composed  of  organs — organic,  then,  as  to 
structure.  The  rock  has  no  organs,  therefore  it  is  ?ion- 
organic,  or  is  inorganic.  These  terms  are  used  also  in 
another  sense.  Thus  we  speak  of  honey  as  organic. 
Manifestly,  we  do  not  mean  organic  as  to  structure,  for 
honey  has  no  organs,  but  it  is  the  product  of  the  bee, 
which  is  an  organic  structure;  hence  honey  is  an  organic 
product.  The  nectary  of  a  flower  is  organic  as  to  struc- 
ture, and  the  nectar  which  it  produces  is  organic  in  being 
the  product  of  the  nectary. 

Branches  of  Physiology. — From  these  elementary 
considerations  it  is  evident  that  physiology  has  to  do 
with  plants  and  animals  only — that  is,  with  organic  struc- 
tures and  their  products.  That  branch  of  the  science 
which  treats  of  the  functions  of  plants  is  denominated 
Vegetable  Physiology,  and  that  which  deals  with  the 
functions  of  animals  is  called  Animal  Physiology. 

Vegetable  Physiology. — We  are  concerned  but  indi- 
rectly with  vegetable  physiology,  or  so  far  only  as  its 
study  helps  us  to  understand  some  of  the  more  obscure 
processes  in  animals.  Some  of  these  processes,  being 
simpler  in  plants,  are  more  easily  studied  in  them,  and 
what  is  there  learned  is  of  great  assistance  in  understand- 
ing analogous  processes  in  man.     Thus  a  knowledge  of 


IN  TR  OD  UCTION.  2 1 

fertilization  as  it  occurs  in  the  vegetable  kingdom  aids 
very  much  in  elucidating  the  process  of  reproduction  in 
the  human  species. 

Animal  Physiology. — The  same  organs  in  different 
animals  perform  their  functions  in  different  ways.  Thus 
the  stomach  of  the  cow  and  that  of  the  dog  act  very  dis- 
similarly, and  a  knowledge  of  the  one  would  aid  very 
little  in  acquiring  a  knowledge  of  the  other.  *What  is 
true  of  the  stomach  is  true  of  other  organs  to  a  greater 
or  lesser  degree.  Each  class  of  animals  has  its  own  pecu- 
liarities as  to  functions — that  is,  has  its  own  physiology. 
One  who  intends  to  devote  his  life  to  the  treatment  of 
the  diseases  of  the  lower  animals  must  study  the  func- 
tions of  those  animals,  while  one  who  is  preparing  him- 
self for  the  cure  of  human  diseases  must  understand  the 
functions  of  the  organs  of  the  human  body,  or  Human 
Physiology. 

Many  hints,  it  is  true,  may  be  obtained  by  the  student 
of  human  physiology  from  a  study  of  the  processes 
which  take  place  in  the  lower  animals,  and  many  of  the 
most  valuable  contributions  made  to  physiological  sci- 
ence have  been  based  upon  such  a  study ;  but  it  must 
ever  be  borne  in  mind  that  specific  differences  exist,  and 
that  we  cannot  infer  too  much  from  such  observations. 
Thus  one  who  studies  the  process  of  stomach  digestion 
in  a  ruminant,  such  as  the  cow,  will  make  a  most  serious 
blunder  should  he  suppose  that  the  process  is  the  same 
in  man.  Errors  of  a  similar  character,  though  perhaps 
less  glaring,  have  been  made,  notably  in  the  process  of 
reproduction.  This  process  is  so  obscure  that  many 
opportunities  which  have  presented  themselves  for  in- 
vestigation, both  in  the  lower  and  in  the  higher  animals, 
have  been  seized  upon,  but  theories  which  have  been 


22  •  HUMAN  PHYSIOLOGY. 

accepted  as  proven,  and  which  have  largely  depended  on 
such  observations,  are  now,  in  the  light  of  more  recent 
study,  being  questioned.  Notwithstanding  this  disad- 
vantage, had  it  not  been  for  such  studies  many  of  the 
most  important  facts  of  medical  science  would  have  re- 
mained undiscovered.  Inasmuch  as  functions  cease  with 
life,  these  observations  can  only  be  made  upon  living 
animals.  Vivisection,  therefore,  has  been  of  the  greatest 
benefit  to  the  human  race,  and  those  who  decry  it  are 
daily  reaping  the  results  which  it  has  attained,  and  which 
could  never  have  been  attained  without  it.  Wanton  and 
unnecessary  experiments  are  to  be  condemned,  but  no 
terms  of  praise  are  too  exalted  to  bestow  upon  those 
patient  investigators  who,  through  many  long  years,  have 
laboriously  and  zealously  pursued  their  studies  and  ex- 
periments, with  no  other  end  in  view  than  to  add  to  the 
sum  of  human  knowledge  and  to  contribute  to  the  relief 
of  human  suffering. 

Human  Physiology  Defined. — Human  physiology  is 
the  science  whicJi  treats  of  the  fitnctions  of  the  organs 
of  the  human  body.  This  science,  together  with  anat- 
omy, which  treats  of  structure,  and  with  che?nistry,  which 
treats  of  composition,  lies  at  the  foundation  of  rational 
medicine.  No  one  can  be  a  successful  physician  who 
does  not  understand  at  least  the  more  important  func- 
tions of  the  human  body,  and  the  greater  the  knowledge 
he  possesses  of  physiology,  the  broader  will  be  the  scien- 
tific groundwork  on  which  he  has  to  build.  Disease  is 
a  departure  from  the  normal  or  physiological  condition. 
A  diseased  organ  performs  its  function  in  an  abnormal 
manner,  and  to  succeed  in  correcting  the  diseased  condi- 
tion we  must  first  be  able  to  recognize  this  abnormal  action, 
which  can  only  be  done  by  knowing  how  the  organ  acts 


INTRODUCTION.  23 

in  health ;  that  is,  by  understanding  its  physiology. 
Even  with  this  knowledge  we  may  be  unable  to  accom- 
plish the  desired  object,  for  the  structure  of  the  organ 
may  be  so  changed  that  there  can  be  applied  no  means 
which  will  restore  it  to  its  normal  condition ;  but  we  are 
certainly  more  likely  to  succeed  if  possessed  of  a  know- 
ledge of  its  physiology  than  if  ignorant  of  it.  The  study 
of  human  physiology  is  but  the  study  of  the  human 
functions,  and  when  we  thoroughly  understand  these 
functions  we  have  mastered  the  science. 

Classiflcation  of  Functions. — The  functions  of  the 
body  may  be  classified  and  defined  as  follows  :  i .  Nutri- 
tive Fiinctions,  which  include  those  concerned  directly 
with  the  maintenance  of  the  individual,  such  as  digestion, 
respiration,  circulation,  etc. ;  2.  Nervous  Functions,  which 
include  those  that  bring  the  different  organs  of  the  body 
into  harmonious  relations  with  one  another,  and,  in  addi- 
tion, bring  the  individual,  through  the  special  senses — 
sight,  hearing,  etc. — into  relation  with  the  world  outside 
him  ;  and  3.  Reproductive  Functions,  which  are  concerned 
not  with  the  individual,  but  with  the  species,  which  they 
perpetuate. 

Physiological  Chemistry. — Although  physiology, 
strictly  speaking,  has  nothing  to  do  with  composition, 
still,  as  a  matter  of  necessity  as  well  as  of  convenience, 
it  is  usual  to  preface  the  study  of  the  functions  of  the 
human  body  with  a  greater  or  lesser  consideration  of  its 
composition.  This  consideration  is  necessary,  because, 
as  a  rule,  medical  students  have  an  insufficient  knowledge 
of  this  branch  of  chemistry — physiological  chemistry — 
to  take  up  at  once  the  study  of  the  functions  with  profit, 
and  should  the  attempt  be  made  confusion  and  loss  of 
time  would  inevitably  result.    As  an  illustration  we  may 


24  HUMAN  PHYSIOLOGY. 

refer  to  the  function  or  series  of  functions  by  which  the 
food  is  prepared  for  absorption — that  is,  digestion.  Food 
is  the  material  which  is  taken  into  the  body  to  supply 
the  waste  of  its  tissues,  and  it  must  be  of  such  a  com- 
position as  will  meet  this  want  To  select  the  proper 
food-materials  we  must  know  of  what  the  body  is  com- 
posed, and  what  are  the  changes  which  take  place  in  its 
composition — what  parts  are  wasted.  For  these  reasons 
a  study  of  physiological  chemistry  must  precede  a  study 
of  the  functions  of  digestion.  This  is  but  one  of  many 
illustrations  which  might  be  given  to  show  the  import- 
ance of  prefacing  the  study  of  physiology  proper  with 
a  study  of  the  chemistry  of  the  body  and  of  the  food. 
We  shall,  therefore,  arrange  the  topics  to  be  discussed, 
and  treat  them,  in  the  following  order :  L  Physiological 
Chemistry  ;  II.  Nutritive  Functions  ;  III.  Nervous  Func- 
tions ;    and  IV.  Reproductive  Functions. 


PHYSIOLOGICAL    CHEMISTRY.  2$ 

I.  PHYSIOLOGICAL   CHEMISTRY. 

Physiological  Chemistry,  as  applied  to  the  human 
body,  may  be  defined  as  t/w  science  which  treats  of  the 
ingredients  of  the  human  body  and  of  the  linvian  food. 
These  ingredients  are  spoken  of  by  some  writers  as 
"  proximate  principles,"  by  others  as  the  "  chemical 
basis,"  and  by  still  others  as  "  physiological  ingredi- 
ents." The  latter  term  is  the  one  which  will  be  adopted, 
as  it  is  the  most  expressive. 

If  the  human  body  be  analyzed  into  its  ultimate  chem- 
ical elements,  it  will  be  found  that  of  the  sixty-nine  ele- 
ments known  to  chemists  no  less  thdiW  fourteen  are  found 
constantly  present.  These  elements  are  oxygen,  car- 
bon, hydrogen,  nitrogen,  calcium,  sodium,  potassium, 
iron,  phosphorus,  sulphur,  magnesium,  chlorine,  fluorine, 
and  silicon.  As  fluorine  and  silicon  occur  in  such  small 
proportions,  they  may  be  omitted  from  consideration 
altogether. 

To  obtain  most  of  these  substances  in  their  elementary 
form  such  processes  must  be  adopted  as  will  utterly  destroy 
the  tissues.  In  the  body,  in  its  living  state,  most  of  these 
substances  do  not  exist  in  their  elementary  condition, 
and,  however  interesting  it  may  be  to  know  all  the  facts 
about  them,  still  a  knowledge  of  the  properties  of  these 
elements  does  not  help  to  an  understanding  of  their 
offices  in  the  human  body.  What  is  really  desired  to 
be  known  is,  under  zvJiat  forms  these  elements  exist  in 
the  body  during  life,  and  not  what  can  be  obtained  by 
the  analytical  chemist. 

Chemical  elements  and  physiological  ingredients  are 
not  interchangeable  terms.  A  physiological  ingredient 
may  be  defined  as  a  substance  which  exists  in  the  body 


26  HUMAN  PHYSIOLOGY. 

under  its  own  form.  To  determine,  then,  whether  a 
given  substance  is  or  is  not  a  physiological  ingredient 
of  the  human  body,  it  must  be  ascertained  whether  it 
does  or  does  not  exist  there  under  its  own  form.  For 
instance,  if  it  is  asked  if  carbon  is  a  physiological  ingre- 
dient, before  the  question  could  be  answered  we  should 
have  to  determine  whether  carbon  exists  in  the  body 
under  its  own  form ;  that  is,  as  carbon. 

Chemistry  demonstrates  that  carbon,  as  an  element, 
is  found  in  nature  in  but  three  forms — namely,  as  coal, 
as  the  diamond,  and  as  graphite  or  plumbago.  In  the 
human  body  none  of  these  substances  is  found ;  there- 
fore carbon  does  not  exist  under  its  own  form,  and  con- 
sequently is  not  a  physiological  ingredient,  although 
more  than  one-eighth  of  the  body  is  made  up  of  carbon, 
and  this  amount  can  be  obtained  from  it.  But  this  car- 
bon does  not  exist  under  its  own  form — that  is,  free  or 
uncombined — but  it  is  all  in  a  state  of  combination,  as 
carbonates  or  in  carbohydrates  or  other  forms  of  combi- 
nation, and  when  we  obtain  the  carbon  as  an  element 
these  combinations  are  broken  up  and  the  carbon  is  set 
free.  Water  is  a  physiological  ingredient,  because  it  ex- 
ists in  the  body  under  its  own  form,  and  can  be  obtained 
therefrom  without  the  use  of  such  violent  means  as  are 
necessary  to  destroy  chemical  combinations. 

It  is  exceedingly  important  to  have  a  clear  conception 
of  what  are  and  what  are  not  physiological  ingredients :  all 
that  can  be  learned  of  them  and  their  properties  will  be  of 
assistance,  but  a  knowledge  of  the  properties  of  their 
chemical  elements  will  be  of  no  assistance  in  our  physi- 
ological studies,  for  the  properties  of  a  compound  are 
not  the  sum  of  the  properties  of  its  component  parts. 
One  might  be  thoroughly  conversant  with  the  properties 


INORGANIC  INGREDIENTS. 


V 


of  oxygen  and  hydrogen,  yet  have  no  possible  concep- 
tion of  the  properties  of  water,  which  their  combination 
forms. 

Classification  of  Physiolog-ical  Ingredients. — The 
physiological  ingredients  of  the  human  body  may  be 
classified  as  follows  :  A.  Inorganic  Ingredients ;  B.  Car- 
bohydrates ;  C.  Fatty  Acids,  Fats,  and  Allied  Sub- 
stances ;  D.  Proteids ;  E.  Albuminoids ;  F.  Enzymes ; 
G.  Intermediate  Products ;  H.  Waste  Products ;  and 
I.  Coloring   Matters. 


A.  Inorganic   Ingredients. 


I.  Water. 


2.  Salts 


Sodium 


Potassium 


Calcium  .   . 


Magnesium 


Ammonium 


Chloride. 

Phosphate. 

Diphosphate. 

Sulphate. 

Carbonate. 

Bicarbonate. 

c  Chloride, 
j  Phosphate. 
^-  Sulphate. 
Carbonate. 


I 


r  Phosphate. 
\  Carbonate. 
L  Fluoride. 

(  Phosphate. 
I  Carbonate. 

Chloride. 


3.  Iron      \ 

4.  Silicon  i 


-  not  free. 


28 


HUMAN  PHYSIOLOGY. 


5.  Oxygen. 

6.  Hydrogen. 

7.  Nitrogen. 

8.  Marsh-gas. 

9.  Ammonia. 

10.  Sulphuretted  Hydrogen. 

11.  Hydrochloric  Acid. 

12.  Carbon  Dioxide. 


I.  Water  (HgO). — Water  is  one  of  the  most  important 
of  the  physiological  ingredients.  Its  quantity  is  about 
70  per  cent,  of  the  whole  body,  and  it  is  found  in  all  the 
tissues,  both  solid  and  fluid. 

Quantity  of  Water  in  the  Body. — The  quantity  (per- 
centage) of  water  in  the  body  is  as  follows  : 

Enamel  of  teeth 
Bones    . 


Muscles 
Blood  . 
Milk  . 
Urine  . 
Gastric  juice 
Saliva    .    . 


0.2 
22. 
76. 
78. 
87. 
93-  , 
97- 
99. 


From  this  table  it  will  be  seen  that  while  water  makes 
up  but  a  small  part  of  the  enamel  of  the  teeth,  it  consti- 
tutes by  far  the  greater  part  of  the  saliva.  Between  these 
two  extremes.it  is  present  in  different  tissues  in  varying 
proportions.  It  should  be  said  of  these,  and  of  most 
other  quantities  given  in  physiological  tables,  that  they 
are  not  invariable,  hence  the  analyses  of  different  author- 
ities will  vary.  The  composition  of  the  milk,  for  in- 
stance, is  not  always  the  same ;  therefore  there  will  not 


INORGANIC  INGREDIENTS.  29 

invariably  be  Zj  per  cent,  of  water  present,  but  the  normal 
variations  from  this  figure,  either  above  or  below,  will 
not  be  very  great,  and  these  percentages  may  be  regarded 
as  averages. 

Offices  of  Water. — We  should  naturally  infer  from  the 
large  quantity  of  water  present  in  the  body,  and  from  its 
universal  presence  in  all  the  solids  and  liquids,  that  its 
offices. must  be  important;  and  a  study  of  these  demon- 
strates that  this  is  a  fact.  It  is  the  water  which  gives  to 
fluids  their  fluidity.  Without  this  property  the  blood 
could  not  circulate  through  the  blood-vessels,  nor  dis- 
solve and  hold  in  solution  the  nutritive  materials  which 
it  supplies  to  the  tissues,  nor  carry  the  waste  materials 
to  the  various  organs  whose  duty  it  is  to  eliminate  them. 
Without  water  the  saliva  would  cease  to  be  the  import- 
ant agent  it  is  in  softening  the  food  in  the  mouth  prepar- 
atory to  its  being  swallowed.  In  short,  without  water 
as  an  integral  part  of  the  fluids  of  the  body  these  fluids 
would  cease  to  be  fluids,  and  the  many  and  varied  offices 
which  they  subserve  would  at  once  be  abolished,  and 
life  could  no  longer  be  maintained. 

Equally  important,  though  less  apparent,  are  the  vari- 
ous offices  which  are  subserved  by  water  in  the  solids  of 
the  body.  From  the  above  table  it  is  seen  that  water 
exists  in  the  muscles  to  the  amount  of  76  per  cent.  The 
.striking  property  of  muscles  is  their  power  of  contrac- 
tility, or  ability  to  shorten.  By  the  exercise  of  this  prop- 
erty all  the  movements  of  the  different  parts  of  the  body 
are  accomplished  :  without  this  power  locomotion  would 
be  impossible,  the  movements  of  the  heart  would  cease, 
and  death  would  quickly  supervene.  A  muscle  deprived 
of  its  water  would  cease  to  possess  this  contractile  power 
— in  other  words,  would  lose  its  characteristic  function. 


30 


HUMAN  PHYSIOLOGY. 


As  will  be  seen  later,  the  skin  possesses  most  import- 
ant functions — those,  for  instance,  of  sensation,  of  excre- 
tion, and  of  protection.  All  these  functions  would  be 
destroyed  if  the  water  in  the  skin  were  expelled.  Perhaps 
this  fact  is  nowhere  more  strikingly  evident  than  in 
studying  the  functions  of  the  skin  of  the  palm  of  the 
hand.  The  pliability  of  this  portion  of  the  skin,  by 
which  objects  are  grasped,  and  the  sense  of  touch,  by 
which  it  can  be  determined  whether  they  are  hard  or 
soft,  whether  rough  or  smooth,  whether  hot  or  cold, 
are  both  dependent  on  the  presence  of  water  in  the  skin, 
and  the  mere  evaporation  of  the  water  would  at  once 
make  the  skin  hard  and  rigid,  its  pliability  would  vanish, 
and  its  functions  would  cease. 

Sources  of  Watei\ — The  water  which  exists  in  the 
body  is  derived  from  two  principal  sources  :  first,  from 
the  food,  and  second,  from  its  formation  in  the  interior 
of  the  body,  the  former  being  the  main  source  of  sup- 
ply. As  water  is  a  constituent  part  of  every  tissue  of 
the  human  body,  so  it  is  of  all  the  varieties  of  food,  both 
solid  and  liquid,  taken  into  the  body. 

The  Quantity  of  Water  in  Food  (percentage)  is  as 
follows : 

Wheat  bread  (fresh) 33, 


Mackerel  .  .  . 
Lean  beef  .  . 
Potatoes  .  .  . 
Human  milk  . 
Cow's  milk  .  . 
Green  vegetables 


70. 
70. 

87.09 
87.41 
88. 


From  this  table  it  will  be  seen  that  the  greater  part  of 
potatoes  and  of  green  vegetables  is  water,  and  that  even 
of  bread,  water  constitutes  at  least  a  third.     In  some 


INORGANIC  INGREDIENTS.  3  I 

vegetables,  such  as  the  turnip,  about  90  per  cent,  is 
water.  In  other  words,  three  of  every  four  pounds  of 
potatoes  and  one  of  every  three  pounds  of  bread  are 
water.  In  the  hquid  food,  as  milk,  tea,  and  coffee,  the 
proportion  of  water  is,  of  course,  still  greater.  The 
amount  of  water  daily  taken  into  the  body  in  solid 
and  liquid  food  aggregates  2000  c.  c.  In  addition  to 
this  there  is,  as  abov^e  stated,  a  small  amount  actually 
formed  within  the  body. 

One  of  the  important  ingredients  of  food  is  the 
class  of  carbohydrates.  A  study  of  their  composition 
shows  that  hydrogen  and  oxygen  exist  in  these  sub- 
stances in  such  proportion  as  to  form  water.  In  the 
various  changes  which  these  elements  undergo  in  the 
body,  water  is  formed.  Besides  this  source  there  is 
reason  to  believe  that  a  small  quantity  of  water  is  formed 
by  the  action  of  free  oxygen  on  some  organic  substances. 
The  amount  of  water  daily  formed  in  these  two  ways  is 
not  far  from  500  c.c,  which  makes,  with  the  water  taken 
in  with  the  food,  a  total  of  2500  c.c. 

Avenues  of  Discharge  from  the  Body. — The  water 
which  has  been  shown  to  form  so  essential  a  part  of  the 
body  is  not,  however,  a  permanent  ingredient ;  that  is, 
while  water  is  always  present,  it  is  not  the  same  water  : 
that  which  at  one  time  exists  in  the  tissues  is  soon  re- 
placed by  other  water.  The  amount  daily  discharged  is 
equal  to  the  amount  taken  in  with  the  food  and  formed 
in  the  body — that  is,  about  2500  grammes.  The  avenues 
by  which  it  passes  out,  and  the  proportion  by  each  are 
as  follows : 

Large  intestines,  as  faeces  ....    4  per  cent. 

Lungs,  as  watery  vapor 20       " 

Skin,  as  perspiration 30       " 

Kidneys,  as  urine 46       " 


32  HUMAN  PHYSIOLOGY. 

When  discharged  it  is  not  pure  water,  but  contains  in- 
gredients that  vary  according  to  the  channel  by  which 
it  is  ehminated.  The  composition  of  these  ingredients 
respectively  will  be  studied  in  its  appropriate  place. 

2.  Salts. — Sodium  chloride,  or  common  salt  (NaCl), 
is  present  in  all  the  solids  and  fluids.  The  quantity  (per- 
centage) in  different  solids  and  fluids  is  as  follows : 

Milk 0.03 

Saliva 0.15 

Gastric  juice 0.17 

Perspiration O.22 

Blood 0.33 

Urine 0.55 

Bones 0.70 

The  total  quantity  of  common  salt  in  the  human  body 
is   no  grammes. 

Offices  of  Sodium  CJiloridc. — The  most  important  office 
which  sodium  chloride  subserves  is  in  connection  with  the 
process  known  as  "  osmosis,"  or  the  diffusion  of  liquids 
through  animal  membranes.  A  second  office  which  it  pos- 
sesses is  to  hold  in  solution  the  globulins.  These  glob- 
ulins are  proteids  which  are  not  soluble  in  distilled  water, 
as  are  the  native  albumins,  but  are  soluble  in  dilute  solu- 
tions of  sodium  chloride  (i  per  cent).  The  importance  of 
this  office  of  common  salt  will  be  more  fully  appreciated 
in  the  study  of  the  plasma  of  the  blood,  of  which  these 
globulins  form  an  essential  part.  A  third  office  which 
is  attributable  to  it  is  to  aid  in  the  excretion  of  waste 
matter. 

Source  of  Sodium  Odoride. — The  food  taken  into  the 
body  is  the  principal  source  of  the  sodium  chloride 
which  the  body  contains. 


INORGANIC  INGREDIENTS.  33 

The  quantity  (percentage)  of  this  salt  in  some  articles 
of  food  is  as  follows : 

Oats o.oi 

Turnips O.03 

Potatoes 0.04 

Cabbage 0.04 

Beets      0.06 

It  has  been  the  opinion  of  physiologists  that  sodium 
chloride  is  not  present  in  sufficient  amount  in  human  food 
to  satisfy  the  demands  of  the  body ;  consequently,  that  an 
additional  amount  must  be  taken  in  as  a  condiment  at  the 
table  or  be  added  to  the  food  during  the  process  of  cook- 
ing. But  Dr.  F.  A.  Cook,  surgeon  to  the  first  Peary 
North-Greenland  Expedition,  states  that  the  Eskimos  who 
dwell  between  the  seventy-sixth  and  seventy-ninth  paral- 
lels use  no  salt  or  condiment  of  any  kind  in  their  food, 
which  is  entirely  of  meat  and  blubber  only  one-third 
cooked.  This  cooking  is  done  vc\.  order  that  there  may 
be  obtained  the  blood  of  the  meat,  and  this  blood  the 
Eskimos  drink.  However  this  may  be  with  the  Eskimos, 
it  is  the  general  experience  that  by  the  addition  of  salt  the 
food  is  not  only  made  more  palatable,  but  the  digestive 
juices  are  also  increased  and  digestion  improved.  This 
insufficiency  of  .salt  in  the  food  of  man  is  seen  also  in  that 
of  some  of  the  lower  animals.  While  carnivora,  or  flesh- 
eating  animals,  find  in  their  food  all  the  salt  they  need, 
it  is  different  with  the  herbivora,  or  vegetable-eaters. 
Especially  noticeable  is  this  fact  in  the  ruminants.  Bous- 
singault  many  years  ago  demonstrated  this  by  a  series 
of  experiments  which  he  conducted.  He  selected  two 
sets  of  bullocks  as  nearly  as  possible  in  the  same  con- 
dition of  health,  and  to  both  sets  he  gave  the  same  food, 
3 


34  HUMAN  PHYSIOLOGY. 

except  that  to  one  he  gave  salt,  while  to  the  other  he 
gave  none.  Several  months  elapsed  before  any  very- 
marked  difference  could  be  detected,  but  at  the  end  of  a 
year,  during  which  time  the  experiment  continued,  there 
were  striking  differences  in  the  two  sets.  The  bullocks 
that  received  the  salt  were  in  excellent  physical  condi- 
tion, while  those  deprived  of  it  were  much  inferior  in 
every  respect :  their  hide  was  rough,  their  hair  tangled, 
and  they  were  dull  and  apathetic. 

Avenues  of  Discharge. — Sodium  chloride  is  daily  dis- 
charged from  the  body  through  the  following  channels 
and  in  the  given  amounts:  urine,  13  grammes;  perspira- 
tion, 2  grammes.  There  is  a  small  amount  also  in  mu- 
cous secretions. 

Sodiitni  Phosphate  (Na2HP04)  and  Potassium  Phosphate 
(K2HPO4). — 'These  salts  are  so  intimately  associated  that 
they  may  be  described  together.  They  are  frequently 
spoken  of  as  the  "  alkaline  phosphates,"  and  they  exist 
in  all  the  solids  and  fluids  of  the  body. 

Offices  of  Alkaline  Phosphates. — The  most  important 
office  which  these  salts  perform  is  to  assist  in  giving 
alkalinity  to  the  alkaline  fluids — a  property  which,  in 
the  blood  at  least,  is  essential  to  life,  and  in  some  of  the 
other  fluids  is  necessary  to  the  performance  of  their 
functions.  The  fluids  of  the  body  are,  with  but  four  ex- 
ceptions, alkaline  in  reaction  :  these  exceptions  are  gastric 
juice,  perspiration,  urine,  and  vaginal  mucus.  The  fol- 
lowing fluids  are  alkaline  :  plasma  of  the  blood  ;  lymph  ; 
aqueous  humor ;  cephalo-rachidian  fluid ;  pericardial 
fluid ;  synovia ;  mucus  (except  that  of  vagina) ;  milk ; 
spermatic  fluid;  tears;  saliva;  bile;  pancreatic  juice; 
and  intestinal  juice. 

The  alkalinity  of  the  plasma  of  the  blood  is  not  an 


INORGANIC  INGREDIENTS.  35 

accidental  property.  The  fact  that  the  blood  of  all  ani- 
mals hitherto  examined  has  invariably  been  found  alka- 
line would  seem  to  indicate  that  this  condition  is  an 
important  one.  Bernard  has  shown  that  if  an  acid  be 
injected  into  the  blood  of  an  animal  death  will  be  pro- 
duced, even  though  the  amount  injected  is  not  enough 
to  make  the  blood  itself  acid.  One  of  the  properties 
of  the  blood  is  to  carry  carbonic  acid  gas — one  of  the 
products  of  the  waste  of  the  tissues — to  the  lungs,  where 
it  is  eliminated  ;  and  experiment  has  shown  that  the 
alkalescence  of  the  blood  enables  it  to  carry  more  of 
this  gas  than  it  could  were  it  neutral  in  reaction.  In 
discussing  the  alkaline  carbonates  it  will  be  seen  that 
they  take  part  in  rendering  alkaline  the  fluids  in  which 
they  occur. 

Source  of  Alkaline  Phosphates. — The  alkaline  phos- 
phates are  taken  into  the  body  in  the  food,  of  which 
they  form  a  constituent  part. 

Avenues  of  Discharge. — After  fulfilling  their  offices  in 
the  body  these  alkaline  salts  are  discharged  in  the  per- 
spiration, the  mucus,  and  the  urine.  In  the  urine  a  por- 
tion of  the  sodium  phosphate  is  converted  into  sodium 
biphosphate,  or,  as  it  is  sometimes  called,  "acid  sodium 
phosphate,"  which  gives  to  the  urine  its  acid  reaction. 
In  this  fluid  are  discharged  daily  4.5  grammes  of  the 
alkaline  phosphates  and  the  sodium  biphosphate. 

Sulphates. — Sodium  sulphate  (NagSOJ  and  potassium 
sulphate  (KgSO^)  are  found  in  the  blood,  lymph,  aque- 
ous humor,  milk,  saliva,  mucus,  perspiration,  urine,  and 
faeces.  Their  quantity  is  small,  however,  except  in  the 
urine,  by  which  fluid  they  are  discharged  daily  to  the 
amount  of  4  grammes. 

Source  of  Sulphates. — These  sulphates  are  taken  in  as 


36  HUMAN  PHYSIOLOGY. 

part  of  the  solid  food  we  eat  and  also  in  the  water  we 
drink.  They  are  present  in  flesh,  in  eggs,  in  the  cereals, 
and  in  other  animal  and  vegetable  foods.  Drinking-water 
often  contains  these  sulphates,  and  the  sulphate  of  lime  as 
well.  Sulphates  are  undoubtedly  formed  to  some  extent 
within  the  body.  In  discussing  the  constitution  of  the 
albuminous  ingredients  of  the  food  it  will  be  seen  that 
one  of  their  elements  is  sulphur.  Some  of  this  sulphur 
becomes  oxidized,  forming  sulphuric  acid,  which,  being  a 
stronger  acid  than  carbonic,  displaces  it  from  the  car- 
bonates and  unites  with  the  alkaline  bases,  forming 
sulphates. 

Carbonates. — Sodium  carbonate  (NagCOg),  sodium  bicar- 
bonate (NaHCOg)  and  potassium  carbonate  (KjCOg)  are 
salts  which  are  known  as  the  "  alkaline  carbonates,"  and 
are  intimately  associated  with  the  alkaline  phosphates. 

Source  of  Carbonates. — These  salts  are,  to  some  extent, 
introduced  with  the  food,  but  are  principally  formed  by 
the  decomposition  of  the  salts  of  the  vegetable  acids. 
In  fruits,  such  as  apples  and  cherries,  and  in  vegetables, 
such  as  potatoes  and  carrots,  are  found  malic,  tartaric, 
and  citric  acids,  united  with  sodium  and  potassium 
to  form  tartrates  and  citrates  of  sodium  and  potas- 
sium. When  these  fruits  or  vegetables  are  eaten,  these 
salts  are  taken  up  by  the  blood,  and  while  in  the  blood 
the  organic  acids  are  decomposed,  and  the  bases  uniting 
with  carbonic  acid,  alkaline  carbonates  are  formed,  which 
are  discharged  in  the  urine.  This  accounts  for  the  fact 
that  after  eating  sufficient  of  such  fruits  or  vegetables 
the  urine  becomes  alkaline. 

Office  of  Carbonates. — The  alkalinity  of  the  blood  and 
of  other  alkaline  fluids  is,  as  has  been  stated,  only  par- 
tially due  to  the  alkaline  phosphates.    In  causing  this  re- 


INORGANIC  INGREDIENTS.  37 

action  the  alkaline  carbonates  have  a  share.  In  the  blood 
of  flesh-eating  animals  the  phosphates  are  more  abundant, 
this  being  due  to  the  predominance  of  phosphates  in  mus- 
cular tissue,  while  in  that  of  the  herbivora  the  carbonates 
are  in  excess  of  the  phosphates.  Remembering,  then, 
what  has  been  said  of  the  formation  of  the  carbonates 
from  the  salts  in  fruits  and  vegetables,  this  difference  in 
the  blood  is  readily  understood.  In  human  blood  there 
are  both  phosphates  and  carbonates  to  account  for  its 
alkalinity. 

Potassmm  Chloride. — Potassium  chloride  (KCl)  is  found 
in  many  of  the  tissues,  especially  in  the  muscles,  in  blood- 
corpuscles,  and  in  milk.  This  salt  occurs  also  in  gastric 
juice,  in  urine,  and  in  perspiration.  Like  sodium  chlo- 
ride, it  is  neutral  in  reaction  and  is  soluble  in  water. 

Source  of  Potassmm  Chloride. — Potassium  chloride  is 
contained  in  both  animal  and  vegetable  foods. 

Avenues  of  Discharge. — Potassium  chloride  is  dis- 
charged in  mucus,  in  urine,  and  in  perspiration. 

Calcium  Salts. — Calcium  phosphate,  lime  phosphate, 
or  phosphate  of  lime  (Ca3(P04)2). — Next  to  water,  calcium 
phosphate  is  the  most  abundant  physiological  ingredient 
of  the  human  body.  Its  total  amount  is  2400  grammes 
in  a  man  weighing  65  kilogrammes. 

The  quantity  (percentage)  of  calcium  phosphate  is  as 
follows : 

Blood 0.03 

Urine 0.07 

Milk 0.27 

Bone 57.6 

Enamel  of  teeth 88.5 

The  greater  part  of  the  calcium  phosphate  in  the  body 


38 


HUMAN  PHYSIOLOGY. 


is  in  the  bones.  It  is  estimated  that  6.4  per  cent,  of  the 
body  is  bone,  and  in  a  man  weighing  65  kilogrammes,  an 
average  weight,  there  would  therefore  be  2400  grammes 
of  this  salt  Its  presence  in  the  fluids  of  the  body  is  not 
in  noteworthy  amount,  except  in  the  milk. 

Office  of  Calcium  Phosphate. — The  principal  office  of 
calcium  phosphate  is  to  give  the  bones  their  rigidity. 
During  early  life  this  salt  is  in  small  amount  in  the 
bones,  and  at  this  time  the  bones  are  soft  and  yielding. 
Later,  as  the  phosphate  is  deposited  in 
greater  amount,  these  structures  become 
more  rigid  and  better  adapted  to  sustain 
weight.  In  old  age  this  salt  is  in  excess 
of  the  organic  ingredients  of  the  bone,  and 
at  this  period  of  life  the  bones  are  easily 
broken,  much  as  a  pipe-stem ;  while  in 
infancy  the  bones  bend,  but  do  not  break, 
or  if  they  do  break  the  fracture  is  not 
complete,  but  is  similar  to  that  which 
occurs  in  a  green  stick,  commonly  known 
as  the"  green-stick  fracture"  (Fig,  i). 
The  flexible  condition  of  the  bones  may 
be  artificially  produced  by  putting  a  long 
bone,  like  the  fibula,  into  a  jar  containing 
dilute  hydrochloric  acid.  The  acid  dissolves  the  calcium 
phosphate,  and,  although  in  appearance  the  bone  is  much 
the  same  as  before,  it  will  now  be  found  so  flexible  as  to 
permit  its  being  tied  in  a  knot  (Fig.  2).  In  the  blood, 
calcium  phosphate,  which  is  insoluble  in  alkaline  fluids, 
is  held  in  solution  by  the  albuminous  constituents.  Were 
these  withdrawn  the  calcium  phosphate  would  at  once 
be  rendered  insoluble,  and  would  be  precipitated. 
Source  of  Calcium  Phosphate. — Calcium  phosphate  is 


Fig.  I.  Partial  or 
"green-stick"  frac- 
ture (Stimson). 


INORGANIC  INGREDIENTS. 


39 


an  important  ingredient  of  the  animal  and  vegetable 
food  of  man.  It  is  contained  in  flesh,  in  eggs,  in  milk, 
in  wheat,  in  oats,  in  rice,  in  peas,  in  beans,  in  potatoes, 
in  apples,  in  cherries,  and  in  other  alimentary  substances. 
Its  presence  in  milk  needs  especial  comment.  As  has 
been  stated,  during  early  life  calcium 
phosphate  is  in  the  bones  in  small  amount. 
The  milk,  upon  which  the  growing  child 
relies  for  its  nourishment,  supplies  the 
necessary  amount  of  this  salt  to  give  the 
bones  their  firmness  and  rigidity.  From 
this  statement  it  will  be  seen  that  the  adul- 
teration of  milk  with  water,  even  though 
the  water  is  pure,  may  be  of  great  injury 
to  the  child.  To  obtain  the  necessary 
amount  of  calcium  phosphate  a  certain 
amount  of  milk  must  be  taken.  If  half 
this  amount  be  water,  the  quantity  of  the 
lime-salt  present  will  be  but  one-half  of 
what  it  should  be,  and  the  child  is  conse- 
quently defrauded.  Of  course,  if  impure 
water  be  used  in  the  adulteration,  there  is 
the  additional  danger  of  introducing  the 
germs  of  disease  with  the  milk. 

Avenues  of  Discharge. — A  very  small 
amount  of  calcium  phosphate  is  dis- 
charged from  the  body — a  fact  which 
shows  its  permanent  character.  It  is  dis- 
charged in  the  urine,  in  the  faeces,  and  in 
the  perspiration. 

Calcium  Carbonate  (CaCOj). — This  salt 
exists    in    the    bones   to   the   amount   of 

...  Fig,  2.   lione  tied  in 

about  300  grammes,  m  the  teeth,  m  the  Knot. 


40  HUMAN  PHYSIOLOGY. 

blood,  in  lymph,  in  chyle,  in  the  saliva,  and  sometimes 
in  the  urine.  Like  calcium  phosphate,  with  which  it  is 
usually  associated,  it  is  insoluble  in  water;  and  when 
it  exists  in  solution  its  solubility  is  due  either  to  alka- 
line chlorides  or  to  free  carbonic  acid. 

Calcium  Fluoride  (CaFlg)  exists  in  bones  and  in  the 
teeth,  and  is  of  little  importance. 

Magnesium  Salts. — Magnesium  phosphate  (MggPOJ 
is  found  wherever  calcium  phosphate  is  found,  and  the 
two  together  are  frequently  spoken  of  as  the  "  earthy 
phosphates."     It  is  discharged  by  the  urine. 

Magnesium  Carbo?iate  (MgCOg). — A  trace  of  this  salt 
is  found  in  the  blood. 

Ammonium  Salts. — Traces  of  ammonium  chloride 
(NH4CI)  are  found  in  the  gastric  juice  and  in  the 
urine. 

3.  Iron. — Iron  is  present  in  the  haemoglobin  of  the 
blood,  in  the  hair,  the  bile,  and  the  urine.  Its  presence 
in  the  coloring  matter  of  the  blood  is  its  most  striking 
characteristic.  It  exists  in  the  blood  combined  with  the 
other  chemical  elements,  and  not  as  an  oxide.  The  total 
amount  of  iron  in  the  blood  of  the  body  of  a  man  weigh- 
ing 65  kilogrammes  is  about  2.71  grammes. 

Office  of  L'07i. — The  office  of  iron  is  not  understood. 
It  is  regarded  as  a  remarkable  fact  that  without  iron 
chlorophyll,  the  green  coloring  matter  of  plants,  cannot 
be  formed — in  other  words,  that  vegetable  life  is  inter- 
fered with ;  and  it  is  believed  that  its  presence  in  the 
coloring  matter  of  the  blood  of  an  animal  is  equally 
necessary  for  its  nutrition. 

Source  of  Iron. — All  animal  food  containing  blood  con- 
tains iron.  In  addition,  animal  food  is  taken  into  the 
body  in  rye,  barley,  oats,  wheat,  peas,  and  strawberries. 


CARBOHYDRA  TES.  4 1 

Avenues  of  Discharge. — A  small  amount  only  of  iron 
is  discharged  in  the  bile  and  the  urine.  After  serving  its 
purpose  in  the  blood  it  is  probably  deposited  in  the  hair. 

4.  Silicon  (S). — It  is  not  known  in  exactly  what  form 
silicon  exists  in  the  body,  possibly  as  silicic  acid. 

5.  Oxygen  (O). — This  gas  is  absorbed  from  the  air, 
and  exists  in  the  blood  principally  in  loose  combination 
with  the  haemoglobin,  though  some  of  it  is  doubtless  free. 

6.  Hydrogen  (H). — This  gas  is  found  in  the  aliment- 
ary canal  and  in  the  expired  air,  having  been  ab- 
sorbed by  the  blood  from  the  intestine. 

7.  Nitrogen  (N). — Nitrogen  is  absorbed  from  the  air 
by  the  blood,  in  which  it  exists  in  a  dissolved  state. 
Some  nitrogen  is   formed  also  within  the  body. 

8.  Marsh  Gas  (CH^). — This  gas  is  found  in  the  ex- 
pired air,  like  hydrogen,  having  been  absorbed  from  the 
intestines.  Reiset  found  that  30  litres  were  expired  in 
twenty-four  hours. 

9.  Ammonia  (NH3). — A  small  amount  of  ammonia  is 
found  in  the  expired  air,  probably  derived  from  the 
blood. 

10.  Sulphuretted  Hydrogen  (HgS). — This  gas  is 
found  in  the  intestines. 

11.  Hydrochloric  Acid  (HCl). — This  acid  exists  in 
gastric  juice. 

1 2.  Carbonic  Dioxide  (CO2). — This  gas  exists  in  many 
of  the  fluids,  having  been  absorbed  by  them  from  the  tis- 
sues.    It  is  also  present  in  blood  and  in  expired  air. 

B.  Carbohydrates. 
This  class   is  so  called  because  its  members  contain 
carbon  united  with  hydrogen  and  oxygen  in  the  propor- 
tion to  form  water.     To  be  placed  in  this  class  a  sub- 


42 


HUMAN  PHYSIOLOGY. 


Stance  must  have  at  least  6  atoms  of  carbon  in  its  mole- 
cule. The  carbohydrates  either  possess  a  sweet  taste, 
as  is  the  case  with  the  sugars,  or,  if  they  do  not,  they 
are  convertible  into  sugars.  They  also  have  the  power 
of  rotating  a  ray  of  polarized  light. 

The  following  table  contains  the  groups  which  form 
this  class,  and  the  members  of  each  group : 

Starch. 


I.  Starch  Group J 


Soluble  starch. 
Erythrodextrin. 
Achroodextrin. 
Maltodextrin. 
Glycogen. 
^  Cellulose. 


2.  Dextrose  Group 


r  Dextrose. 

J  Lsevulose. 
I  Galactose. 
L  Inosit. 


3.  Cane-sugar  Group 


C  Saccharose. 
\  Maltose. 
L  Lactose. 


I.  Starch  Group. 

Starch  {C^^f)^^. — The  exact  formula  for  starch  is 
not  determined.  Chemists  agree  that  it  is  not  CgH^oOs, 
but  some  multiple  of  this,  as  indicated  by  "  ?z,"  and  that 
"  n "  is  not  less  than  five.  Starch  is  not  found  in  the 
human  body,  except  when  it  is  taken  in  as  food.  It  is 
very  abundant  in  vegetable  food.  Indeed,  it  is  said  that 
starch  exists  in  every  chlorophyll-containing  plant  at 
some  period  of  its  existence.    Starch  is  a  substance  of 


CARB  OH  YDRA  TES. 


43 


great  interest,  from  the  fact  that  it  is  the  first  organic  sub- 
stance produced  by  vegetables  from  inorganic  matter. 
Animals  have  not  the  power  to  produce  organic  sub- 
stances directly  from  members  of  the  inorganic  kingdom, 
but  plants  have,  and  they  exercise  this  power,  and  from 
the  organic  materials  thus  produced  animals  are  nour- 
ished. Plants  may  change  the  organic  matter  from  one 
form  to  another,  as  starch  to  sugar,  but  were  inorganic 
substances  alone  supplied  to  animals  they  would  starve. 
The  inorganic  substances  out  of  which  the  plant  forms 
the  starch  are  carbonic  acid  and  water,  these  being  taken 
from  the  atmosphere  and  the  soil.  This  process  is  re- 
presented by  the  following  chemical  formula : 
{6CO,  +  sH^O)^  =  {C,U,,0,\  -f  0„ 

Carbonic  acid.       Water.  Starch.  Oxygen. 

That  is,  the  carbonic  acid  and  the  water  are  decomposed, 
the  carbon  and  hydrogen,  with  some  of  the  oxygen, 
unite  and  form  starch,  while  the  rest  of  the  oxygen  is 
set  free.  To  bring  about  this  change  there  must  be 
present  solar  light  and  the 
green  coloring  matter,  chlo- 
rophyll. If  chlorophyll  be 
absent,  this  change  does  not 
take  place,  nor  does  it  when 
solar  light  is  absent. 

Starch  exists  in  plants  in 
the  form  of  grains,  known  as 
"  starch-grains  "  or  "  .starch- 
granules  "  (Fig.  3).  They 
present  a  characteristic  ap- 
pearance under  the  micro- 
scope by  which  they  may 
at  once  be  recognized.     Each  granule  presents  a  number 


Fig.  3.  Starch-grains. 


44 


HUMAN  PHYSIOLOGY. 


of  concentric  markings  and  varies  in  size  and  shape  in 
different  plants ;  by  these  points  of  difference  the  plant 
from  which  the  granules  are  derived  may  be  identified. 
This  fact  is  made  use  of  in  detecting  adulterations,  in 
which  cheaper  kinds  of  starch  are  mixed  with  more  ex- 
pensive kinds  and  sold  for  the  latter  at  a  higher  price. 
The  markings  are  caused  by  the  arrangement  of  the 
material  composing  the  granule  in  alternating  layers  of 
cellulose  and  granulose. 

Quantity  of  Starch. — The  quantity  of  starch  (percent- 
age) in  the  following  food-plants  is 


Sweet  potatoes 
Potatoes 
Beans  . 
Peas  .  . 
Wheat  . 
Oats 
Rye    .  . 
Indian  corn 
Rice     .    . 

The  presence  of  starch 


16.05 
20. 

33- 

37-30 
57.88 
60.59 
64.65 

67.55 
88.65 


is  determined  by  the  addition 
of  a  little  tincture  of  iodine,  which  gives  a  blue  color. 
This  reaction  is  due  to  the  granulose,  and  not  to  the 
cellulose.  Starch  cellulose  differs  in  some  respects  from 
ordinary  cellulose,  as  is  demonstrated  by  its  solubility 
in  some  reagents  which  do  not  dissolve  the  latter. 

Starch  is  insoluble  in  cold  water,  but  when  boil- 
ing water  is  added  to  it  in  an  amount  twenty  times 
its  weight,  the  granules  swell  and  burst  and  there  is 
formed  a  gelatinous  mass  which  is  called  "  starch-paste." 
This  paste  will  respond  to  the  iodine  test,  showing  it  to 
be,  principally  at  least,  granulose.     If  the  amount  of 


CARB  O  HYDRA  TES.  45 

water  added  should  be  one  hundred  times  the  weight  of 
the  starch,  a  solution  of  granulose  is  made,  the  insoluble 
cellulose  falling  to  the  bottom  of  the  vessel.  This  starch 
solution  will  likewise  respond  to  the  iodine  test. 

Soluble  Starch,  or  Aniylodcxtrin  (C6Hio05)„. — When 
starch-paste,  produced  in  the  manner  above  described, 
is  heated  to  a  temperature  of  40°  C.  on  a  water-bath, 
and  saliva  is  then  added,  the  paste  changes  from  a  gelat- 
inous to  a  watery  condition,  and  in  this  fluid  soluble 
starch  now  exists.  This  soluble  starch  gives  also  a  blue 
color  with  iodine.  It  filters  readily,  whereas  starch-paste, 
even  in  dilute  solution,  filters  with  difficulty.  Soluble 
starch  is  dextro-rotatory;  that  is,  it  rotates  the  ray  of 
polarized  light  to  the  right.  This  substance  is  the  first 
product  of  the  conversion  of  starch  into  sugar  by  saliva, 
and  if  the  action  be  not  stopped,  as  it  may  be  by  boiling, 
the  stage  of  soluble  starch  is  only  a  temporary  one,  it 
passing  quickly  into  that  of  dextrin.  As  will  be 
seen  hereafter,  the  ingredient  of  the  saliva  that  changes 
starch  into  soluble  starch  is  a  ferment — ptyalin — the 
action  being  one  of  hydrolysis.  Pancreatic  juice  pro- 
duces the  same  change  as  does  saliva,  and  as  the  action 
of  saliva  is  due  to  the  ferment  ptyalin,  so  is  the  action  of 
pancreatic  juice  due  to  a  ferment,  amylopsui,  both  of 
which  substances  belong  to  the  ferments  or  enzymes. 

Erythrodextrin  (CgHi^Or,),!. — If  the  action  of  either  of 
these  ferments  upon  starch  be  not  arrested  in  the  soluble- 
starch  stage,  erythrodextrin  is  formed.  The  blue  color 
caused  by  the  action  of  iodine  on  starch  gradually 
changes  into  violet,  reddish-violet,  and  then  to  reddish- 
brown  as  the  starch  gradually  changes  to  erythrodextrin. 
This  reddish-brown  color  produced  by  iodine  is  the  test 
for  erythrodextrin. 


46  HUMAN  PHYSIOLOGY. 

Achroodextrin  (CgHjoOgX. — If  the  action  of  these  fer- 
ments be  continued,  a  still  further  change  in  the  starch 
takes  place.  It  passes  into  the  condition  of  achro- 
odextrin, and  iodine  fails  to  produce  any  color.  A  further 
change  into  maltose  follows  the  formation  of  achro- 
odextrin. In  the  action  of  these  ferments  upon  starch 
outside  the  body  the  first  product  is  a  mixture  of  dextrin 
with  the  sugar,  but  within  the  body  there  is  little  doubt 
but  that  all  the  starch  is  converted  into  sugar,  and  as 
such  is  absorbed.  If  starch  be  treated  with  boiling  dilute 
acids  instead  of  with  these  enzymes,  the  changes  just 
described  take  place  with  far  greater  rapidity,  and  dex- 
trose results. 

Maltodextrin  (CeHioOs)^. — If  diastase,  the  ferment  con- 
tained in  malt  extract,  be  used  instead  of  saliva  or  pan- 
creatic juice,  maltodextrin  is  formed;  and  indeed  it  is  not 
certain  that  the  latter  substance  is  not  formed  in  ad- 
dition to  the  erythrodextrin  and  achroodextrin  when 
saliva  and  pancreatic  juice  are  employed.  Maltodextrin 
differs  from  the  dextrins  already  described  in  being  more 
soluble  in  alcohol,  in  being  diffusible,  and  in  responding 
to  Fehling's  test.  It  also  passes  over  into  maltose  by 
the  continued  action  of  the  diastase. 

Glycogen  (CgHjyOs)™. — The  similarity  between  glyco- 
gen and  starch  has  led  to  the  term  "  animal  starch  "  be- 
ing applied  to  the  former.  Glycogen  was  first  discovered 
in  the  liver,  but  has  since  been  found  to  exist  in  the 
integument  and  the  mucous  membranes  of  the  human 
embryo,  in  the  placenta  and  the  amnion,  in  white  blood- 
corpuscles  and  in  pus-corpuscles,  in  oysters  and  in  other 
mollusca.  For  purposes  of  study  it  is  usually  obtained 
from  the  liver  of  an  animal  (a  rabbit  or  a  dog),  in  which 
it  is  stored  up  in  amorphous  granules  around  the  nuclei 


CARB  O  HYDRA  TES.  47 

of  the  liver-cells.  Glycogen  is  soluble  in  water,  and 
with  iodine  gives  a  port-wine  color.  This  color  does 
not  distinguish  it  from  erythrodextrin,  but  when  it  exists 
pure,  as  ordinarily  it  does  not,  it  is  precipitated  by  60 
per  cent,  alcohol,  while  the  dextrins  are  not  precipitated. 
Watery  solutions  are  dextro-rotatory. 

In  general  it  may  be  said  that  the  action  of  the 
enzymes  and  of  boiling  acids  upon  glycogen  is  the  same 
as  upon  starch.  The  glycogen  of  the  liver  becomes  con- 
verted, by  physiological  processes,  into  liver-sugar,  which 
is  regarded  as  identical  with  dextrose.  In  this  process 
probably  no  maltose  is  formed,  such  as  occurs  in  the  ar- 
tificial hydrolysis  already  described.  This  difference 
would  seem  to  indicate  that  in  the  liver-cells  there  is 
no  ferment  to  which  this  action  can  be  attributed,  for,  so 
far  as  can  be  judged,  most  ferments  produce  maltose,  and 
not  dextrose,  and  up  to  the  present  time  no  dextrose-pro- 
ducing ferment  has  been  obtained  from  the  liver. 

Cellulose  (C6Hi,j05)„. — Nowhere  in  the  animal  body  is 
cellulose  found,  but  it  exists  in  many  of  the  vegetable 
alimentary  principles  upon  which  man  relies  for  his 
nutrition.  As  has  already  been  stated,  it  is  a  constituent 
of  the  starch-granule,  and  while  in  the  raw  state  it  is  un- 
affected by  the  digestive  fluids,  yet  when  it  is  boiled  it 
becomes  converted  into  sugar  as  well  as  the  granulose. 
While  cellulose  has  not  a  marked  nutritive  value,  still 
it  is  more  than  probable  that  the  older  view  that  it  is  of 
no  value  as  a  food-stuff  is  erroneous.  It  has  recently 
been  suggested  that  there  is  in  the  alimentary  canal  an 
undiscovered  ferment  which  has  the  power  of  causing 
this  conversion  of  the  cellulose.  This  change  takes 
place  especially  when  those  vegetables  and  fruits  are 
eaten  whose  cell -walls  are  tender  and  have  not  yet  be- 


48  HUMAN  PHYSIOLOGY. 

come  Hgnified  or  woody  in  character.  The  cellulose  of 
some  plants,  such  as  the  date,  is  regarded  as  a  reserve 
material  to  be  made  use  of  in  germination. 

The  presence  of  cellulose  is  recognized  by  the  fact  that 
when  treated  with  strong  sulphuric  acid  it  becomes  con- 
verted into  a  substance  that  is  colored  blue  by  iodine. 
Schulze's  reagent  is  another  test  for  its  presence.  This 
test  consists  in  the  production  of  a  blue  color  when  the 
substance  is  treated  with  iodine  dissolved  to  saturation 
in  a  solution  of  chloride  of  zinc  to  which  potassium 
iodide  has  been  added. 

2.  Dextrose   Group. 

Dextrose{^\xzo's>&,  grape-sugar,  diabetic  sugar)  (CgHigOg) 
is  normally  found  in  the  blood,  chyle,  lymph,  and  in  very 
small  amount  in  the  urine.  In  the  disease  known  as  "  dia- 
betes, mellitus"  the  quantity  of  dextrose  in  the  blood  and 
urine  is  very  much  increased.  It  is  a  substance  of  much 
interest,  as  it  is  in  the  form  of  dextrose  that  the  carbohy- 
drates of  the  food  find  their  way  into  the  blood.  In  its 
pure  state  dextrose  is  colorless  and  readily  crystallizes ; 
it  is  soluble  in  cold  water,  more  so  in  hot  water.  It  is 
dextro-rotatory,  whence  it  derives  its  name.  Dextrose 
reduces  metallic  oxides,  a  property  which  is  made  use 
of  in  determining  its  presence  and  in  measuring  its  quan- 
tity. Tests  based  on  this  are  Trommer's,  Fehling's, 
Moore's,  and  others. 

Fermentations  of  Dextrose. — Dextrose  undergoes  vari- 
ous fermentations:  (i)  Alcoholic;  (2)  Lactic;  and  (3) 
Butyric. 

I.  Alcoholic  Fermentation. — In  alcoholic  fermentation, 
under  the  influence  of  yeast,  the  dextrose  is  decomposed 
and  ethyl  alcohol  and  carbonic.anhydride  are  produced 


CA  RB  OH  YDRA  TES.  49 

(CgHigOg  ^  2C2HgO  +  2CO2).  This  process  is  at  the 
height  of  its  activity  when  the  temperature  is  25°  C. ; 
when  above  45°  C.  or  below  5°  C.  it  ceases.  When 
sugar  is  present  in  the  solution  to  the  extent  of  more 
than  15  per  cent.,  the  process  of  fermentation  will  be 
arrested,  by  the  alcohol  produced,  before  all  the  sugar 
has  been  decomposed. 

2.  Lactic  Ferine ntatioii. — When  milk  sours,  the  sugar 
which  it  contains  is  converted  into  lactic  acid,  constitut- 
ing the  lactic  fermentation  (CgHj.^Og  =  2C3Hg03).  This 
fermentation  is  not  confined  to  milk-sugar,  but  may  occur 
also  with  dextrose.  This  change  is  brought  about  by 
the  presence  of  specific  micro-organisms.  It  is  stated 
that  there  exists  also  in  the  mucous  membrane  of  the 
stomach  an  enzyme  which  can  change  lactose,  and 
possibly  dextrose,  into  lactic  acid. 

3.  Butyric  Fermentation. — When  the  lactic  fermenta- 
tion is  continued  for  some  time,  it  is  liable  to  pass  into 
the  butyric.  This  change  is  due  to  the  action  of  a  fer- 
ment (organized)  upon  the  lactic  acid.  In  the  change 
hydrogen  and  carbonic  anhydride  are  given  off  (2C3Hg03 
=  C3H7.COOH.+  2C02H- 2H2).  The  optimum  (most 
favorable)  temperature  for  the  lactic  and  butyric  fermen- 
tations is  from  35°  C.  to  40°  C.  When  the  diet  consists 
largely  of  carbohydrates,  both  these  fermentations  may 
occur  in  the  alimentary  canal. 

LcBviilose  (left-rotating  sugar,  fruit-sugar,  or  mucin- 
sugar)  (CgHjjOg)  is  found  in  many  fruits  and  in 
honey,  and  is  said  to  occur  occasionally  in  urine.  It 
is  not  crystallizable.  When  cane-sugar  is  treated  with 
dilute  mineral  acids,  it  is  decomposed  into  equal  parts 
of  dextrose  and  laevulose.  Cane-sugar  has  a  dextro- 
rotatory action  on  polarized  light,  but  when  changed  by 
4 


50  HUMAN  PHYSIOLOGY. 

the  acid  the  solution  becomes  laevo-rotatory,  and  the 
cane-sugar  is  said  to  be  "  inverted ;"  hence  the  mixture 
of  dextrose  and  laevulose  is  sometimes  spoken  of  as  "  in- 
vert-sugar." As  will  be  seen  in  the  consideration  of 
cane-sugar,  "  inversion  "  takes  place  in  the  alimentary- 
canal.  Although  in  many  respects  laevulose  is  very 
similar  to  dextrose,  still  its  action  on  polarized  light 
serves  to  distinguish  the  two. 

Galactose  (CgHj^Og). — When  lactose  is  boiled  with 
dilute  mineral  acids  it  is  changed  into  dextrose  and 
galactose : 

QaH^Pn  +  HP  =  CgHi  A  +  CeHj  A 

Lactose.  Dextrose.  Galactose. 

W  hiosit,  or  muscle-sugar  (CgHjaOg  +  2H2O),   has  been 

found  in  the  muscles,  lungs,  liver,  spleen,  kidneys,  and 
brain,  and  pathologically  in  urine.  It  occurs  also  in  beans 
and  grape-juice.  Because  of  its  sweet  taste  and  its  chemi- 
cal composition  it  has  been  regarded  as  a  carbohydrate, 
but  as  it  has  no  rotatory  action  on  polarized  light,  does  not 
reduce  metallic  salts,  and  does  not  undergo  the  alcoholic 
fermentation,  it  is  now  regarded  as  belonging  to  the 
benzol  series,  and  not  as  being  a  carbohydrate.  Its  ability 
to  undergo  lactic  fermentation  is  very  doubtful, 

3.  Cane-sugar  Group. 

Saccharose,  or  cane-sugar  (C12H22O11). — This  sugar 
is  not  found  in  the  human  body,  but  it  nevertheless  plays 
an  important  part  in  the  food  of  man.  It  occurs  in  the 
sugar-cane  and  in  some  other  plants.  It  does  not  reduce 
metallic  salts,  it  is  soluble  in  water,  it  is  dextro-rotatory, 
and  it  does  not  undergo  alcoholic,  but  does  readily  un- 
dergo lactic,  fermentation  in  presence  of  sour  milk  to 


CARB  OH  YD R  A  TES.  5  I 

which  zinc  oxide  is  added  to  fix  the  acid  as  formed. 
One  of  the  interesting  facts  connected  with  saccharose 
is  its  property  of  "  inversion,"  which,  as  we  have  seen, 
consists  in  its  decomposition  into  equal  parts  of  dextrose 
and  laevulose,  and  to  this  mixture  the  name  of  "  invert- 
sugar"  has  been  given.  This  change  is  represented 
chemically  as  follows : 

C12H22O11  +  H2O  —  CgHiaOg  +  CgHjgOg, 

Cane-sugar.  Water.  Dextrose.  Lsevulose. 

and  may  be  produced  by  the  action  of  acid,  as  has 
been  described  under  "  Lsevulose."  It  takes  place 
also  in  the  small  intestine  under  the  influence  of  an 
enzyme  of  the  intestinal  juice — namely,  invcrtiii.  This 
enzyme  exists  also  in  yeast,  where  it  has  the  same  power 
as  in  the  intestinal  juice. 

Cane-sugar  cannot  be  taken  up  as  such  by  the  blood, 
and  when  injected  into  an  animal  it  is  eliminated  un- 
altered in  the  urine.  When  taken  in  as  food  it  is 
absorbed,  not  as  cane-sugar,  but  as  invert-sugar,  into 
which  it  has  been  changed.  This  inversion  is  most  pro- 
nounced in  the  small  intestine ;  it  is  claimed  that  it  may 
take  place  also  in  the  stomach,  and  that  there  exists  in 
the  gastric  juice  an  enzyme  which  has  this  power. 

Maltose  (CjaHgaOu  +  HjO). — In  considering  malto- 
dextrin  it  was  stated  that  starch-paste,  under  the  in- 
fluence of  diastase,  passes  into  maltodextrin,  and,  if  the 
action  be  continued,  into  maltose.  When  starch-paste  or 
glycogen  is  treated  with  .saliva,  malto.se  is  the  principal 
sugar  formed ;  prolonged  treatment  with  pancreatic  juice 
will  produce,  beside  the  maltose,  some  dextrose.  Al- 
though pancreatic  juice,  on  the  one  hand,  acts  in  this 
manner,  still  the  tissue  of  the  small  inte.stine  or  an  ex- 
tract of  it  has  but  slight  action  on  the  paste.     On  the 


52  HUMAN  PHYSIOLOGY. 

other  hand,  the  pancreatic  juice  rapidly  changes  maltose 
into  dextrose.  Maltose,  like  cane-sugar,  injected  into 
the  blood  is  eliminated  as  maltose  in  the  urine.  From 
this  fact  it  would  appear  that  maltose  is  not  absorbed 
as  such  in  the  intestine,  but  as  dextrose ;  and  it  would 
further  appear  that,  inasmuch  as  the  tissue  of  the  intes- 
tine has  this  converting"  power,  the  change  from  maltose 
into  dextrose  occurs  while  the  process  of  absorption 
is  actually  taking  place,  and  not  before.  The  action  of 
pancreatic  juice  on  starch  in  the  intestine  will  be  further 
discussed  in  the  consideration  of  the  ferments  of  this 
fluid 

Maltose  is  soluble  in  water,  but  it  is  less  soluble  in 
alcohol  than  dextrose.  It  is  crystallizable,  dextro-rota- 
tory, and  reduces  metallic  salts.  Maltose  is  distinguished 
from  dextrose  (i)  by  the  difference  in  its  rotatory  power 
on  polarized  light,  that  of  maltose  being  greater ;  (2)  by 
maltose  having  a  less  reducing  power,  as  when  boiled 
with  Fehling's  solution  only  two-thirds  as  much  cuprous 
oxide  is  separated  out  with  maltose  as  with  dextrose ; 
(3)  by  Barfoed's  reagent,  which,  consisting  of  a  solution 
of  cupric  acetate  in  water  to  which  acetic  acid  has  been 
added,  is  reduced  by  dextrose,  but  not  by  maltose. 

Lactose  (milk-sugar,  sugar  of  milk)  (C12H22O11 -f- HgO) 
is  found  only  in  milk,  although  it  has  been  said  to  occur 
in  the  urine  of  lying-in  women  and  in  sucklings.  It  is 
crystallizable,  less  soluble  in  water  than  dextrose,  and 
insoluble  in  alcohol.  It  is  dextro-rotatory,  its  power  in 
this  respect  being  the  same  as  that  of  dextrose.  It  does 
not  reduce  Barfoed's  reagent.  As  above  noted  in  speak- 
ing of  galactose,  lactose  is  changed  into  equal  parts  of 
sugar  and  dextrose  by  boiling  it  with  dilute  mineral 
acids. 


FATTY  ACIDS,   ETC.  53 

Lactose  by  itself  does  not  undergo  alcoholic  fermenta- 
tion with  yeast,  but  an  alcoholic  fermentation  does  take 
place  in  milk,  as  when  mare's  milk  is  used  for  the  prepa- 
ration of  kumyss  and  kephir.  This  fermentation  is  due 
to  special  ferments,  the  nature  of  which  is  not  fully  un- 
derstood. In  Russia  kephir  ferment  may  be  purchased. 
Lactose  readily  undergoes  the  lactic  fermentation.  It  is 
this  change  which  takes  place  in  the  souring  of  milk  due 
to  the  action  of  a  ferment.  The  character  of  the  change  in 
the  case  of  lactose  is  the  same  as  described  in  dextrose 
and  saccharose.  Lactose  injected  into  the  blood  is 
eliminated  by  the  urine,  as  are  saccharose  and  malt- 
ose, and  like  them  must  therefore  be  changed  in  the 
alimentary  canal  during  the  process  of  absorption.  This 
conversion,  which  is  probably  into  dextrose  and  galac- 
tose, takes  place,  as  in  the  case  of  maltose,  while  the 
sugar  is  passing  through  the  walls  of  the  intestines. 

C.  Fatty  Acids,  Fats,  and  Allied  Substances. 

Formic  Acid. — This  acid  has  been  obtained  from  the 
spleen,  thymus  gland,  pancreas,  muscles,  brain,  blood, 
and  urine. 

Acetic  Acid. — Fermentation  of  the  food  in  the  stomach 
may  produce  acetic  acid.  It  has  been  found  in  normal 
and  in  diabetic  urine. 

Acetone. — Diabetic  urine  yields  acetone  on  distilla- 
tion ;  it  is  this  substance  which  gives  the  ethereal  odor 
to  such  urine.  The  blood  of  persons  suffering  from 
diabetes  has  also  been  found  to  contain  it,  and  to  its 
presence  has  been  attributed  the  fatal  coma  which 
comes  on  in  some  cases  of  this  disease.  Acetone  has 
been  found  also  in  the  urine  of  healthy  children,  and 


54  HUMAN  PHYSIOLOGY. 

it  has  been  stated  that  it  has  been  detected  in  their 
breath. 

Propionic  Acid. — This  acid  is  found  in  perspiration,  in 
fermenting  diabetic  urine,  and  it  has  been  found  also 
in  the  contents  of  the  stomach  and  in  normal  urine. 

Normal  Butyric  Acid  is  found  in  perspiration,  in  the 
contents  of  the  large  intestines,  in  the  faeces,  and  in  urine. 
It  occurs  also  during  lactic  fermentation. 

Isobutyric  Acid  occurs  in  faeces,  and  is  one  of  the 
products  of  the  putrefaction  of  proteids. 

Caproic  and  Caprylic  Acids  are  constituents  of  the 
perspiration,  and,  with  Capric  Acid,  are  found  also  in 
butter. 

Neutral  Fats  are  palmitin,  stearin,  and  olcin.  They 
are  regarded  by  chemists  as  compounds  of  glycerin  and 
the  respective  fatty  acid.  Thus  the  acid  of  palmitin  is 
palmitic ;  that  of  stearin,  stearic ;  and  that  of  olein,  oleic. 
They  are  characterized  by  being  insoluble  in  water, 
slightly  soluble  in  alcohol,  and  very  soluble  in  ether 
and  chloroform.  All  fats  are  mixtures  of  the  three  vari- 
eties, the  difference  in  the  consistency  of  any  given  fat 
depending  upon  the  proportion  in  which  the  neutral  fats 
are  present.  Thus  in  the  more  solid  fats,  such  as  suet, 
stearin  predominates,  while  in  the  fluid  fats  it  is  olein 
which  is  in  excess.  There  is  a  difference  also  in  the 
proportions  of  these  substances  in  the  fats  of  different 
animals.  Human  fat  and  that  of  carnivorous  animals 
contain  palmitin  in  excess  over  stearin  and  olein,  while 
in  that  of  the  herbivora  stearin  predominates,  and  in  that 
of  fishes,  olein. 

Source  of  Fat  in  the  Huniari  Body. — Human  fat  is 
derived  from  the  fats,  the  carbohydrates,  and  the  proteids 
of  the  food.     In  fatty  meats,  nuts,  eggs,  milk,  and  other 


FATTY  ACIDS,  ETC.  55 

food  more  or  less  fat  exists  as  a  constituent,  and  un- 
doubtedly contributes  to  the  formation  of  the  fat  of  the 
body.  Food  containing  starch  and  sugar  is  also  fatten- 
ing in  its  nature,  and  persons  who  have  an  excess  of  fat 
are  placed  upon  a  diet  containing  a  minimum  of  these 
ingredients.  Herbivorous  animals — the  cow,  for  instance 
— rely  entirely  upon  vegetable  food  for  their  support, 
and  it  is  the  carbohydrates  which  this  contains  that  are 
converted  into  the  fat  of  their  milk  or  that  which  covers 
their  muscles.  That  proteid  food  will  also  produce  fat 
is  shown  by  the  amount  of  the  latter  which  carnivorous 
animals  put  on. 

Offices  of  Fat. — The  offices  which  fat  subserves  in  the 
human  body  are  manifold  :  (i)  It  protects  the  underlying 
parts  from  injury,  as  in  the  palm  of  the  hand  and  the  sole 
of  the  foot ;  (2)  it  serves  as  a  lubricator,  as  in  the  seba- 
ceous matter  poured  out  upon  the  skin,  which  keeps  it  soft 
and  pliable ;  (3)  it  acts  as  a  non-conductor  of  heat,  aiding 
in  the  retention  within  the  body  of  the  vital  heat,  which 
would  otherwise  be  lost  so  rapidly  as  to  produce  injur- 
ious results ;  (4)  it  serves  as  a  reservoir  when  the  sup- 
ply of  food  is  cut  off  or  diminished ;  thus  in  wasting 
diseases  the  fat  deposited  in  various  parts  of  the  body  is 
absorbed  and  contributes  to  its  nutrition  ;  (5)  it  is  a  source 
of  energy  and  of  heat  through  its  oxidation. 

Important  properties  of  fats,  besides  those  already 
mentioned,  which  deserve  special  consideration,  are  two 
— that  of  forming  a  soap  and  that  of  forming  an  emul- 
sion. 

Saponification. — Fats  are  said  to  be  saponifiable  ;  that 
is,  capable  of  being  converted  into  a  soap.  If  a  fat  be 
heated  with  a  caustic  alkali  under  pressure,  it  splits  up 
into  glycerin,  and  a  fatty  acid  which   unites  with  the 


$6  HUMAN  PHYSIOLOGY. 

alkali,  the  compound  being  a  soap.  Thus,  if  palmitin  be 
the  fat  selected  and  the  alkali  be  sodium,  the  palmitic 
acid,  uniting  with  the  sodium,  would  form  sodium  pal- 
mitate,  a  soap.  If  potassium  were  the  alkali,  the  product 
would  be  potassium  palmitate ;  similarly,  stearin  would 
form  a  stearate,  and  olein  an  oleate.  The  sodium  soaps 
are  hard,  and  those  of  potassium  are  soft.  In  the  dis- 
cussion of  intestinal  digestion  it  will  be  seen  that  the 
process  of  saponification  takes  place  in  the  small  intes- 
tine, and  that  the  soap  there  formed  aids  in  the  import- 
ant functions  of  that  portion  of  the  alimentary  canal, 

Emulsification. — Besides  being  saponifiable,  fats  are 
also  emulsifiable — capable  of  forming  an  emiJlsion.  If 
oil  and  water  be  poured  into  a  test-tube,  they  will  at 
once  separate,  the  oil  floating  on  the  water.  If  the 
mouth  of  the  tube  be  closed  by  the  thumb  and  the  tube 
firmly  shaken,  the  oil  and  water  will  form  a  milky  mix- 
ture, but  will  separate  again  when  the  agitation  ceases ; 
if  a  small  amount  of  an  alkali  be  added  and  the  tube  be 
again  shaken,  the  separation  will  not  take  place  as  before, 
but  the  milky  appearance  will  continue  for  some  con- 
siderable time.  If  a  drop  of  the  mixture  be  placed  under 
the  microscope,  it  will  be  found  that  the  oil-globules  have 
been  broken  up  into  an  exceedingly  fine  state  of  subdi- 
vision, some  of  the  particles  being  too  small  to  measure 
even  with  a  very  high  magnifying  power.  This  more  or 
less  permanent  subdivision  and  suspension  of  the  oil-glob- 
ules constitutes  an  emulsion.  The  change  is  not  a  chem- 
ical one,  but  is  purely  physical.  A  similar  process  takes 
place  in  the  small  intestine  during  intestinal  digestion, 
and  is  a  necessary  preliminary  to  the  absorption  of  fat. 

Lactic  Acid  is  found  in  the  alimentary  canal,  especially 
when  large  quantities  of  carbohydrates  have  been  in- 


PRO  TEWS.  57 

gested.  It  occurs  also  in  muscles,  and  has  been  said  to 
exist  in  the  nerve-cells  of  the  brain.  It  has  already  been 
mentioned  as  the  product  of  lactic  fermentation. 

Sarcolactic  Acid  occurs  in  blood  and  in  muscles ;  to 
the  latter  it  gives  their  acid  reaction. 

Cholesterin. — Chemically,  this  substance  is  an  alcohol, 
the  only  one  found  free  in  the  human  body.  It  occurs 
in  the  bile,  in  the  blood,  in  white  nervous  matter,  and  in 
the  crystalline  lens.  It  is  a  constituent  also  of  the  yolk 
of  ^ZZ^  of  wheat,  Indian  corn,  peas,  and  beans.  It  has 
some  characteristics  of  the  fats,  such  as  insolubility  in 
water  and  solubility  in  ether  and  chloroform,  but  it  is  not 
saponifiable,  and  is  in  other  most  important  respects  un- 
like them.  It  is  classified  here  more  for  purposes  of  con- 
venience than  for  any  affinity  with  other  members  of  the 
class. 

D.  Proteids. 

These  ingredients  compose  the  principal  parts  of  the 

muscles,  the  glands,  and  the  nervous  tissues,  and  of  the 

solids  of  the  blood  they  are  the  most  important.     Their 

percentage  composition  is  as  follows  : 

Carbon  .    .    .    .50.-55.        Hydrogen     .    .    6.9-  7.3 

Nitrogen  .    .    .15.-18.        Oxygen     .    .    .20.  -23.5 

Sulphur 0.3-  2. 

When  proteids  are  burned,  there  is  found  in  the  ash  a 
certain  quantity  of  salts — from  the  ignition  of  egg-albu- 
min, for  instance,  chlorides  of  sodium  and  potassium 
result,  and  salts  of  calcium,  magnesium,  and  iron  in 
small  quantities.  It  is  still  undecided  whether  these 
salts  are  integral  parts  of  proteids  or  impurities. 

Reactions  of  Proteids. — The  presence  or  absence  of 
proteids  is  determined  by  certain  reactions,  three  of  which 
are  given : 


58 


HUMAN  PHYSIOLOGY. 


Xanthoproteic  Reaction. — When  proteids  are  heated 
with  strong  nitric  acid,  they  turn  yellow,  the  color  be- 
coming deep  orange  on  the  addition  of  ammonia,  caustic 
soda,  or  potash. 

Millo7i's  Reaction. — Proteids  when  heated  with  Millon's 
reagent  give  a  white  precipitate  which  becomes  brick- 
red  on  cooling.  This  reagent  is  prepared  by  dissolving 
mercury  in  nitric  acid  and  adding  water.  The  precipi- 
tate which  forms  is  allowed  to  settle,  and  the  fluid  is  the 
reagent.  Very  small  amounts  of  proteids  give  the  red 
color  without  the  precipitate. 

Piotrowski s  Reaction. — When  a  proteid  is  mixed  with 
an  excess  of  concentrated  solution  of  sodium  hydrate 
and  one  or  two  drops  of  a  dilute  solution  of  cupric  sul- 
phate, a  violet  color  is  produced  which  becomes  deeper 
on  boiling. 

Classification. — The  proteids  are  classified  as  follows  : 

XT  ^-        ii_       •  f  Egg-albumin. 

I.  Native  albumms \   c 

I  berum-albumm. 

Acid-albumin. 

Syntonin. 

Alkali-albumin. 

Casein. 

Crystallin. 

Vitellin. 

Paraglobulin. 

3.  Globulins \   Serum-globulin. 

Fibrinogen. 

Myosin. 

Globin. 

4.  Albumoses.  8.  Intermediate  products. 

5.  Peptones.         7.  Enzymes.    9.  Waste  products. 

6.  Albuminoids.  10.  Coloring  matters. 


2.  Derived  albumins 


P ROTE  IDS.  59 

1.  Native   Albumins. 

Native  albumins  are  found  in  the  solids  and  fluids 
of  the  body.  They  are  soluble  in  water,  and  are  coagu- 
lated by  heat  at  from  65°  to  73°  C,  coagulation  taking 
place  more  readily  if  dilute  acetic  acid  be  present.  They 
are  not  precipitated  by  alkaline  carbonates,  by  chloride  of 
sodium,  the  solution  of  neutral  salts  in  general,  or  by 
dilute  acids. 

Egg- Albumin. — As  its  name  implies,  egg-albumin  is 
obtained  from  the  white  of  egg.  If  much  of  it  be  taken 
in  the  food  or  if  it  be  injected  into  the  blood,  part  of  it 
appears  in  the  urine.  When  shaken  with  ether  it  is  pre- 
cipitated. Nitric  acid,  heat,  and  the  prolonged  action 
of  alcohol  coagulate  egg-albumin,  and  mercuric  chloride, 
nitrate  of  silver,  and  lead  acetate  precipitate  it,  forming 
insoluble  compounds. 

Serum- Albumin. — Serum-albumin  occurs  in  the  blood, 
in  lymph,  in  chyle,  in  milk,  and  in  some  pathological 
fluids.  When  albumin  is  found  in  the  urine  it  is- gener- 
ally serum-albumin.  Serum-albumin  differs  from  egg- 
albumin  in  not  readily  being  coagulated  by  alcohol  or 
precipitated  by  ether,  and  in  not  appearing  in  the  urine 
when  injected  into  the  blood. 

2.  Derived  Albumins. 

The  members  of  this  group  are  sometimes  spoken  of 
as  "  albuminates."  They  are  insoluble  in  distilled  water 
and  in  dilute  neutral  saline  solutions,  but  are  soluble  in 
acids  and  alkalies.  Their  solutions  are  not  coagulated  by 
boiling. 

Acid- Albumin. — When  a  solution  of  either  of  the  native 
albumins  is  treated  with  a  dilute  acid — hydrochloric  acid, 


60  HUMAN  PHYSIOLOGY. 

for  instance — it  is  converted  into  acid-albumin.  In  this 
conversion  it  undergoes  important  changes.  Its  solution 
is  not  coagulated  by  heat,  and  when  it  is  neutralized  the 
proteid  is  precipitated.  The  conversion  from  the  native 
to  the  acid-albumin  is  gradual,  and  is  hastened  by  heat, 
care  being  taken  that  the  temperature  is  not  sufficiently 
high  to  coagulate  it.  Globulins  are  likewise  converted 
into  acid-albumins  by  the  same  means,  but  more  readily, 
while  coagulated  proteids  or  iibrin  require  the  acid  to  be 
concentrated.  Each  proteid  produces  its  own  special 
acid-albumin,  although  the  difference  between  them  is 
very  slight. 

Syntonin. — Syntonin  is  the  special  acid-albumin  which 
results  from  the  action  of  acids  on  myosin — the  globulin 
which  occurs  in  muscles.  It  is  of  special  interest  as  be- 
ing the  acid-albumin  formed  in  the  stomach  during  the 
digestion  of  muscular  tissue.  It  is  soluble  in  lime-water, 
and  this  solution  is  partially  coagulated  by  boiling ;  it  is 
insoluble  in  acid  sodium  phosphate  (NaHgPOJ,  while 
other  acid-albumins  are  soluble.  It  differs  from  alkali- 
albumin  in  that  when  acid  sodium  phosphate  is  present 
and  an  alkali  is  added  it  does  not  pass  into  solution  until 
the  whole  of  the  acid  phosphate  salt  has  been  converted 
into  the  neutral  phosphate  (NagHPO^),  while  alkali-albu- 
min is  soluble  before  this  change  takes  place. 

Alkali- Albumin. — If  a  native  albumin  be  treated  with 
a  dilute  alkali  in  the  manner  described  in  the  treatment 
with  a  dilute  acid,  it  will  be  converted  into  alkali- 
albumin,  as  in  the  former  instance  when  an  acid  was 
used  it  was  changed  into  acid-albumin.  The  alkali-albu- 
min, like  the  acid-albumin,  is  not  coagulated  by  heat; 
when  neutralized  the  proteid  is  precipitated,  and  the 
precipitate,  which  is  insoluble  in  water  and  in  neutral 


PRO  TEWS-  6 1 

solution  of  sodium  chloride,  is  dissolved  by  dilute  acids 
or  alkalies. 

Some  writers  have  regarded  acid-  and  alkali-albumin 
as  differing  from  each  other  only  in  that  in  the  one  case 
the  proteid  is  united  with  an  acid,  and  in  the  other  case 
with  a  base ;  but  more  recent  investigations  seem  to 
show  that,  though  closely  related,  they  are  in  reality 
distinct,  and  that  what  was  said  of  the  product  of  the 
action  of  acids  on  proteids  is  probably  true  of  that  of 
alkalies — namely,  that  each  proteid  yields  its  own  product, 
although  as  yet  they  cannot  well  be  distinguished.  Acid- 
albumin  can  be  converted  into  alkali-albumin  by  strong 
alkalies,  but  alkali-albumin  cannot  be  changed  into  acid- 
albumin  by  the  action  of  acids.  In  1838,  Mulder  de- 
scribed a  substance  which  he  called  "protein."  This 
designation  is  now  abandoned.  It  has  been  suggested 
that  what  he  called  "  protein  "  might  have  been  alkali- 
albumin. 

Casein  exists  in  human  milk  in  from  0.18  to  1.90  per 
cent.,  the  mean  being  0.63  per  cent.,  and  in  that  of  the 
cow  in  from  1.17  to  7.40  per  cent,  3.01  per  cent,  being 
the  mean.  This  derived  albumin  occurs  only  in  milk. 
It  has  been  suggested  that  this  physiological  ingredient 
should  be  called  "  caseinogen,"  and  that  the  term  "  case- 
in" should  be  restricted  to  the  curd  formed  when  milk 
coagulates  under  the  influence  of  rennin,  the  ferment  in 
rennet.  Inasmuch  as  we  speak  of  "  fibrinogen "  and 
"  fibrin,"  the  former  before  and  the  latter  after  coagula- 
tion, the  suggestion  is  well  worthy  of  consideration  as 
tending  to  simplification.  Casein  is  precipitated  by  acids 
and  by  rennet  at  40°  C,  and  it  contains  0.847  P^^  cent. 
of  phosphorus.  When  pure  it  is  a  fine  snow-white 
powder  insoluble   in  water,  but  is   soluble  in  alkalies, 


62  HUMAN  PHYSIOLOGY. 

carbonates  and  phosphates  of  the  alkahes,  hme-  and 
baryta-water. 

As  has  already  been  stated,  casein  clots  under  the  in- 
fluence of  the  enzyme  rennin,  but  alkali-albumin,  which 
has  been  regarded  by  some  as  identical  with  casein,  does 
not.  Milk  from  which  casein  has  been  removed  by  pre- 
cipitation still  contains  a  small  amount  of  a  coagulable 
proteid — lactalbuniin — very  similar  to  serum-albumin, 
but  not  identical.  Upon  the  surface  of  milk  exposed 
for  some  time  to  a  temperature  above  50°  C.  a  pellicle 
forms,  which  is  stated  by  some  chemists  to  be  casein, 
by  others  lactalbumin.  This  formation  takes  place  more 
rapidly  if  a  stream  of  air  be  blown  over  the  surface  of 
the  milk. 

What  has  been  said  of  casein  applies  especially  to  that 
obtained  from  cow's  milk.  The  differences  between 
cow's  milk  and  human  milk,  so  far  as  regards  casein,  are 
as  follows  :  I.  Human  milk,  when  it  clots  at  all  with  ren- 
nin, does  so  less  firmly  than  cow's  milk ;  2.  Acids  very 
imperfectly  precipitate  the  casein  from  human  milk :  to 
do  this  completely  magnesium  sulphate  must  be  used  to 
the  point  of  saturation;  3.  The  casein  of  human  milk  is 
less  soluble  in  water  than  that  of  cow's  milk. 


3.  Globulins. 

Globulins  are  insoluble  in  distilled  water,  but  are  solu- 
able  in  dilute  saline  solutions,  as,  for  instance,  i  per  cent, 
sodium  chloride,  in  very  dilute  acids  and  alkalies.  If 
the  saline  solutions  be  saturated,  the  globulins  will  be 
precipitated.  If  the  acid  or  the  alkali  be  not  dilute,  but 
strong,  the  globulins  will  be  converted  into  acid-albu- 
min or  into  alkali-albumin. 


PROTEIDS.  63 

Crystallin  (globulin)  is  the  globulin  of  the  crystalline 
lens. 

Vitellin  is  the  proteid  of  the  yolk  of  eggs.  An  identi- 
cal globulin  has  been  obtained  from  vegetable  proto- 
plasm. In  the  Q.^%,  vitellin  is  associated  with  lecithin, 
and  indeed  up  to  the  present  time  vitellin  has  never 
been  obtained  free  from  lecithin.  It  has  been  said  to 
occur  in  the  chyle  and  in  the  amniotic  fluid. 

Paraglobjilin  {?,Qx\xvc\-^<:kivX\Vi\  fibrino-plastin  ;  serum- 
casein)  exists  in  blood-plasma  to  the  amount  of  from  2 
to  4  per  cent.,  and  also  in  lymph,  in  chyle,  and  in  serous 
fluids  like  the  fluid  in  hydrocele.  In  urine  there  has 
been  found  a  globulin  which  is  apparently  identical  with 
paraglobulin. 

Fibrinogen. — The  plasma  of  blood  contains  fibrinogen, 
as  do  also  chyle  and  serous  fluids.  Like  paraglobulin, 
it  is  contained  in  the  fluid  of  hydrocele.  It  is  of  great 
physiological  interest,  as  the  clotting  of  blood  consists 
in  the  conversion  of  fibrinogen  into  fibrin.  For  purposes 
of  study  fibrin  is  usually  obtained  by  whipping  blood 
with  twigs  or  with  wires.  The  material  that  clings  to 
these  is  fibrin,  together  with  some  of  the  white  and  red 
corpuscles  of  the  blood,  which  are  entangled  in  the 
meshes  of  the  fibrin.  When  washed  in  water  the  red 
coloring-matter  is  washed  out  and  the  fibrin  is  colorless. 
Fibrin  is  insoluble  in  water  and  in  dilute  saline  solutions. 
In  dilute  acids — as,  for  instance,  hydrochloric  acid — it 
swells  up  and  becomes  transparent.  If  it  be  left  in  the 
acid  for  a  long  time  or  if  the  temperature  be  raised  to  40° 
C,  it  is  changed  into  acid-albumin. 

Myosin. — When  a  muscle  passes  into  the  condition 
known  as  rigor  mortis  or  "  cadaveric  rigidity,"  this  change 
is  due  to  a  coagulation  or  clotting  of  the  material  of 


64  HUMAN  PHYSIOLOGY. 

which  the  muscle  consists,  the  clot  being  myosin.  It 
has  been  suggested  that  this  substance  should,  before 
coagulation,  be  called  "myosinogen,"  and  after  coagula- 
tion "myosin,"  just  as  "fibrinogen"  and  "fibrin"  are 
spoken  of.  It  will  be  remembered  that  an  acid  acting 
on  myosin  converts  it  into  syntonin. 

Globin. — When  exposed  to  the  air  for  a  sufficient 
time  haemoglobin,  the  red  coloring-matter  of  the  blood, 
decomposes,  and  globin  is  one  of  the  products.  Globin 
is  very  slightly  soluble  in  dilute  acids,  alkalies,  and  solu- 
tions of  sodium  chloride,  but  is  converted  into  acid-  and 
alkali-albumin  by  strong  acids  and  alkalies  respectively. 


4.  Albumoses. 

If  a  proteid  be  acted  upon  by  pepsin  in  the  presence 
of  0.2  per  cent,  of  hydrochloric  acid,  a  portion  of  it  is- 
changed  into  an  acid-albumin.  Some  writers  regard 
this  as  syntonin,  but  the  tendency  at  the  present  time 
is  to  apply  the  name  of  "  syntonin  "  only  to  that  partic- 
ular acid-albumin  formed  by  the  action  of  acid  on  myosin. 
It  has  also  been  spoken  of  as  "  parapeptone,"  but  the 
two  are  not  identical,  as  is  evident  from  the  fact  that 
parapeptone  is  incapable  of  being  converted  into  peptone 
by  the  action  of  pepsin.  Subsequently,  if  the  action  of 
the  pepsin  be  continued,  this  acid-albumin  disappears  and 
parapeptone  and  albumoses  are  produced.  Still  later  in 
the  process  these  albumoses  are  changed  into  peptones. 

If  instead  of  pepsin  and  hydrochloric  acid  the  proteid 
be  treated  with  trypsin,  one  of  the  enzymes  of  pancreatic 
juice,  and  a  0.25  per  cent,  solution  of  sodium  carbonate, 
alkali-albumin  is  formed,  and  later  albumoses,  which  are 
changed  into  peptones,  some  of  which  still  later  are  con- 


PROTEIDS.  65 

verted  into  leucin  and  tyrosin.  The  albumoses,  then, 
are  intermediate  products  in  the  conversion  of  proteids 
into  peptones.  The  theory  of  Kiihne  is  that  in  the  diges- 
tion of  a  proteid  two  albumoses  are  formed,  anti-albu- 
mose  and  hemi-albumose. 

Anti-albumose  is  practically  not  distinguished  from 
acid-albumin  or  syntonin ;  the  further  action  of  the 
digestive  ferment  converts  it  into  antipeptone. 

Hemi-albumose  is  identical  with  what  has  been  called 
"  propeptone."  It  occurs  occasionally  in  the  urine,  and 
is  found  also  in  the  marrow  of  bones  and  in  cerebro- 
spinal fluid.  Under  the  further  influence  of  the  ferment 
it  passes  into  hemipeptone.  Hemi-albumose  is  regarded 
by  some  writers  as  being  composed  of  four  forms  of 
albumose :  i,  protalbumose ;  2,  deutero-albumose ;  3, 
hetero-albumose ;  4,  dysalbumose ;  but  this  is  not  yet 
determined.  This  subject  is  further  discussed  in  treat- 
ing of  Digestion. 

Albumoses  have  of  late  assumed  a  position  of  great 
importance,  for  the  reason  that  they  have  been  found  to 
possess  peculiar  properties  which  were  never  before  sus- 
pected. The  poison  of  the  cobra,  regarded  as  the  most 
virulent  of  animal  poisons,  is  an  albumose.  When  cer- 
tain albumoses  are  injected  into  the  blood  its  coagula- 
bility may  be  destroyed  and  death  may  result.  This 
action  was  formerly  attributed  to  peptones,  but  it  is  now 
believed  to  be  due  to  the  albumoses  in  the  peptones. 
Immunity  from  certain  diseases  has  been  brought  about 
by  the  protective  influence  of  certain  albumoses  which 
have  been  produced  by  the  action  of  the  germs  of  those 
diseases,  so  that  in  this  group  of  substances  there  is  a 
variety  of  members,  some  beneficial  and  some  poisonous. 
Albumoses  also  occur  in  plants,  as  wheat  and  the  papaw. 


66  HUMAN  PHYSIOLOGY. 

5.  Peptones. 

In  no  part  of  physiological  chemistry  has  more  valu- 
able work  been  done  than  in  the  study  of  this  group  of 
physiological  ingredients,  one  important  result  being  to 
show  that  what  have  been  described  as  peptones  are  in 
reality  mixtures  of  albumoses  and  peptones. 

True  peptones  are  very  soluble  in  water,  and  are  not 
precipitated  by  boiling  nitric  acid,  by  acetic  acid,  or 
by  potassium  ferrocyanide.  They  are,  however,  precip- 
itated from  neutral  or  feebly-acid  solutions  by  mercuric 
chloride,  tannic  acid,  bile-acids,  and  phospho-tungstic 
acid.  They  give  Millon's  and  the  Biuret  reaction,  are 
very  diffusible,  and  are  laevo-rotatory.  In  stating  that 
peptones  are  very  diffusible  it  must  also  be  stated  that 
this  is  true  when  they  are  compared  with  other  proteids, 
but  when  the  comparison  is  made  with  crystalline  sub- 
stances, such  as  sodium  chloride,  peptones  are  not  very 
diffusible. 

As  has  already  been  seen,  antipeptone  is  the  peptone 
which  results  from  the  action  of  the  digestive  ferments 
— pepsin  or  trypsin — on  anti-albumose,  and  hemipeptone 
is  that  which  results  from  their  action  on  hemi-albumose. 
The  latter  yields  leucin  and  tyrosin  with  the  further 
action  of  trypsin  ;  the  former  does  not,  though  the  action 
of  the  ferment  be  prolonged. 

E.  Albuminoids. 

The  albuminoids  resemble  the  proteids  in  their  com- 
position ;  some  of  them  contain  no  sulphur.  They  are 
neither  crystallizable  nor  diffusible. 

Mucin. — Mucus,  the  product  of  mucous  glands,  owes 
its  peculiar  ropy   consistency  to   the  ingredient  mucin. 


ALBUMINOIDS.  67 

Mucin  contains  carbon,  hydrogen,  nitrogen,  and  oxygen, 
but  no  sulphur.  It  is  derived  from  the  proteids,  and 
exhibits  Millon's  and  the  Xanthoproteic  reactions.  When 
treated  with  mineral  acids  an  acid-albumin  is  formed,  and 
at  the  same  time  there  is  produced  a  carbohydrate  which 
may  yield,  when  treated  with  acid,  a  reducing  sugar. 
On  account  of  these  two  products  which  result  from  the 
action  of  an  acid  on  mucin,  it  has  been  regarded  by  some, 
although  probably  incorrectly,  as  a  mixture  of  a  proteid 
and  a  carbohydrate. 

It  has  been  assumed  that  the  mucin  of  different  fluids 
is  the  same  substance,  but  that  it  is  slightly  modified  in 
each  instance.  This  has  not  been  proved ;  indeed,  the 
weight  of  evidence  rather  favors  the  view  that  there  are 
several  mucins,  differing  in  certain  particulars.  Mucin  is 
an  ingredient  of  bile,  but  is  not  found  in  that  fluid  while 
it  is  still  in  the  liver.  It  is  added  to  the  bile  while  in 
the  gall-bladder,  and  is  secreted  by  the  lining  membrane 
thereof  Mucin  dissolves  in  water  and  is  precipitated  by 
acetic  acid  and  by  alcohol. 

Gelatin. — When  connective  tissues  are  boiled  in  water 
for  a  considerable  time,  especially  in  a  Papin  digester, 
they  yield  a  substance  which  is  called  "  gelatin."  It  has 
been  assumed  that  there  is  in  bone  a  substance  which  has 
been  named  "  ossein,"  and  that  in  the  ordinary  connec- 
tive tissues  there  is  another  substance  called  "  collagen  ;" 
moreover,  that  the  gelatin  is  not  an  original  constituent 
of  the  tissues,  but  is  the  product  of  these  two  substances 
after  the  boiling.  This  assumption  has  much  to  sustain 
it,  for  if  tendons  be  treated  with  trypsin,  everything  will 
be  dissolved  but  the  collagen,  and  if  bones  be  treated 
with  cold  dilute  acid,  the  salts  will  be  dissolved  and  the 
ossein  will    remain.      These  two    substances — collag^en 


68  HUMAN  PHYSIOLOGY. 

and  ossein — are  insoluble  in  water,  in  saline  solutions, 
in  cold  dilute  acids,  and  in  alkalies.  If,  however,  they 
be  boiled  in  water  for  a  long  time,  they  are  changed 
into  gelatin,  which  when  it  cools  forms  a  jelly  or  "  gela- 
tinizes." When  this  gelatin  is  dry  it  forms  a  transparent 
brittle  substance  which  is  familiar  as  glue  or  as  the 
gelatin  used  in  food. 

Gelatin  is  insoluble  in  cold  water,  but  swells  up  in  it, 
and,  when  the  water  is  warmed,  dissolves.  It  is  precipitated 
by  tannic  acid  and  mercuric  chloride,  but  not  by  acids, 
by  alum,  nor  by  the  salts  of  silver,  iron,  copper,  or  lead. 
Its  percentage  composition  is  carbon,  50.76 ;  hydrogen, 
7.15  ;  oxygen,  23.21  ;  nitrogen,  18.32  ;  sulphur,  0.5.  The 
sulphur  is  believed  to  be  due  to  impurities,  and  is  not 
regarded  as  a  constituent  of  pure  gelatin.  By  compar- 
ing this  analysis  with  that  of  the  proteids  the  difference 
will  be  seen. 

If  collagen  be  boiled  in  water  for  a  longer  period  than 
is  sufficient  to  convert  it  into  gelatin,  the  latter  will  be 
converted  into  gelatin-peptones.  This  same  change 
takes  place  if  gelatin  be  treated  with  pepsin  in  presence 
of  an  acid  or  with  trypsin,  and  the  same  conversion  takes 
place  in  the  stomach.  Gelatin-peptones  are  more  solu- 
ble than  gelatin,  and  are  diffusible.  It  will  be  remem- 
bered that  in  noting  the  action  of  the  enzymes,  pepsin 
and  trypsin,  upon  proteids,  albumoses  were  formed  as 
intermediate  products  before  the  final  formation  of  pep- 
tones. Likewise,  when  gelatin  is  changed  into  gelatin- 
peptones  there  are  intermediate  products,  to  which  the 
name  of"  gelatoses"  has  been  given.  Gelatin  is  digested 
and  absorbed  in  man  and  is  a  valuable  food-stuff,  but 
does  not  supply  the  tissues  with  nitrogen,  as  its  nitrogen 
cannot  be  built  up  into  that  of  a  proteid. 


ALBUMINOIDS.  69 

Chondrin. — As  gelatin  is  looked  upon  as  a  product  of 
the  prolonged  boiling  in  water  of  collagen  and  ossein,  so 
chondrin  is  regarded  as  resulting  from  a  similar  treat- 
ment of  "  chondrigen,"  the  matrix  of  hyaline  cartilage. 
Chondrigen  is  insoluble  in  water,  but  when  boiled  in 
a  Papin  digester  it  is  dissolved  gradually  and  is  trans- 
formed into  chondrin,  which  gelatinizes  on  cooling. 
The  percentage  composition  of  chondrin  is  carbon, 
50.9;  hydrogen,  7.1;  nitrogen,  14.9;  oxygen,  29;  sul- 
phur, 0.4.  It  is  precipitated  by  acetic  acid,  which  does 
not  redissolve  the  precipitate.  Mineral  acids  in  small 
amounts  produce  a  precipitate  which  dissolves  in  excess 
of  the  acids.  Chondrin  is  also  precipitated  by  alum  and 
by  the  salts  of  silver,  iron,  and  lead.  There  is  some 
evidence  showing  that  chondrin  is  a  mixture  of  mucin 
and  gelatin,  but  this  combination  is  not  conclusively 
determined. 

Elastin. — This  substance  is  an  ingredient  of  elastic  tis- 
sue, as,  for  instance,  the  ligamentum  nuchae.  Its  per- 
centage composition  is  carbon,  55.6 ;  hydrogen,  'j.'j  ;  nitro- 
gen, 17.7;  oxygen,  21.1  ;  it  does  not  contain  sulphur, 
Elastin  is  soluble  only  when  boiled  in  strong  alkalies  at 
100°  C.  If  boiled  with  sulphuric  acid  at  100°  C.,it  is  not 
only  dissolved,  but  is  also  decomposed,  yielding  from  30  to 
40  per  cent,  of  leucin  and  0.25  per  cent,  of  tyrosin.  Elastin 
is  digested  under  the  influence  of  pepsin  in  an  acid,  and 
trypsin  in  an  alkaline  medium,  but  it  is  doubtful  whether 
elastin  passes  into  the  stage  of  peptone,  but  rather  does 
not  go  beyond  the  intermediate  stage  of  what  may  be 
termed  "  elastoses." 

Keratin. — This  substance  is  found  in  all  horny  tissues, 
such  as  hair,  nails,  and  epidermis.  Its  percentage  com- 
position  is  carbon,   52.5;    hydrogen,  7;    nitrogen,    17; 


JO  HUMAN  PHYSIOLOGY. 

oxygen,  25  ;  sulphur,  5.  Keratin  is  dissolved  by  alka- 
lies, and  the  sulphur  forms  sulphides  of  the  metals.  It 
is  unaffected  by  the  action  of  pepsin  or  trypsin. 

F.  Enzymes. 

There  are  two  classes  of  enzymes  or  ferments  :  (i)  or- 
ganized ferments,  of  which  yeast  is  an  example,  and  (2) 
unorganized  or  soluble  ferments,  of  which  pepsin  is  an 
example.  It  has  been  proposed  to  limit  the  term  "  fer- 
ment "  to  the  organized  class,  and  to  denominate  the 
changes  which  its  members  cause  in  substances  upon 
which  they  act  as  "  fermentation,"  while  to  the  soluble 
or  iinoj'ganized  class  to  apply  the  name  of  "  enzyme," 
and  to  give  to  the  process  for  which  its  members  are 
responsible  the  term  "zymolysis."  There  will  here  be 
discussed  only  the  unorganized  ferments  or  enzymes. 

Some  of  the  enzymes  on  analysis  have  been  found  to  be  , 
very  similar  in  their  composition  to  the  proteids,  although 
containing  less  carbon.  This  similarity  is  shown  in  the 
percentage  composition  of  trypsin.  The  unorganized 
enzymes  are  soluble  in  water  and  in  glycerin,  and  are 
precipitated  by  an  excess  of  absolute  alcohol,  but  are 
not  diffusible.  Minute  quantities  of  unorganized  en- 
zymes under  proper  conditions  will  bring  about  zymo- 
lytic  changes  in  considerable  quantities  of  the  substances 
upon  which  they  act,  apparently  without  diminishing. 
The  conditions  under  which  they  act  vary  for  each 
enzyme,  but  as  a  rule  high  temperatures  destroy  and 
low  temperatures  inhibit,  while  for  each  there  is  a  tem- 
perature at  which  its  action  is  the  most  pronounced  ; 
this  is  called  the  "  optimum "  temperature.  Thus  for 
pepsin  the  optimum  temperature  is  from  35°  to  40°  C, 
while  below  1°  C.  its  action  ceases,  as  it  does  also  at 


ENZYMES.  71 

70°  C,  while  boiling  permanently  destroys  it.  It  has 
been  determined,  however,  that  when  perfectly  dry  the 
enzymes  may  be  heated  to  160°  C.  without  destroying 
their  power. 

An  interesting  fact  also  connected  with  the  enzymes 
is,  that  when  they  have  produced  a  considerable  amount 
of  their  product  their  action  is  diminished,  and  that  if 
this  new  product  accumulates  still  more,  the  zymolytic 
action  of  the  enzymes  may  be  brought  to  an  end,  although 
their  power  to  act  would  still  be  present  if  these  products 
were  removed.  In  some  instances  the  enzyme  is  not  the 
direct  product  of  the  cells,  but  the  cells  form  what  is 
termed  a  "  zymogen,"  which  is  afterv/ard  converted  into 
the  enzyme.  Each  zymogen  is  named  from  the  enzyme 
which  it  produces  :  thus  the  zymogen  of  trypsin  is 
"  trypsinogen,"  that  of  pepsin  is  "  pepsinogen,"  etc.  It 
is  an  interesting  and  valuable  fact  that  chloroform  in- 
hibits the  action  of  the  organized  ferments,  but  does  not 
interfere  with  that  of  the  unorganized.  As  it  is  very  im- 
portant to  have  a  clear  idea  of  the  meaning  of  certain 
terms  which  occur  repeatedly  in  the  discussion  of  the 
enzymes  and  their  action,  these  terms  will  here  be  de- 
fined— namely : 

Amylolytic  Enzyme. — The  conversion  of  starch  into 
sugar  is  an  amylolytic  change,  and  an  enzyme  which  has 
the  power  of  producing  this  change  is  an  amylolytic 
enzyme. 

Diastatic  or  Diastasic  Ensymc. — There  exists  in  barley 
an  enzyme,  diastase,  which  has  the  power  of  changing 
starch  into  sugar  ;  the  change  itself,  and  also  the  en- 
zyme, are  spoken  of  as  diastatic  or  diastasic.  It  will  be 
seen,  therefore,  that  amylolytic,  diastatic,  and  diastasic 
are  synonymous. 


72  HUMAN  PHYSIOLOGY. 

'  Proteolytic  Enzyme. — The  conversion  of  a  proteid  into 
a  peptone  is  a  proteolytic  change,  and  any  enzyme  which 
causes  it  is  a  proteolytic  enzyme. 

Hydrolytic  Enzyme. — It  is  now  generally  accepted  that 
in  the  conversion  of  starch  into  sugar  and  of  proteids 
into  peptones  the  change  consists  in  the  assumption  of 
a  molecule  of  water;  thus, 

Starch.  Water.  Sugar. 

This  change  is  called  "  hydrolysis,"  and  the  action  is 
said  to  be  hydrolytic.  Both  amylolytic  and  proteolytic 
changes  are  hydrolytic.  Indeed,  there  are  reasons  for 
believing  that  the  enzymes  produce  their  action  in  every 
instance  by  causing  the  substances  upon  which  they  act 
to  unite  with  water. 

Ptyalin. — This  enzyme  is  found  in  saliva,  and  is  one 
of  its  important  constituents.  It  is  an  intere.sting  fact 
that  from  many  of  the  tissues  and  fluids  of  the  body 
a  similar  enzyme  may  be  obtained.  This  is  especially 
marked  in  the  pig.  When  ptyalin  is  obtained  from 
saliva  it  is  a  white  powder  which  dissolves  in  water 
and  converts  starch  into  maltose.  This  action  mark- 
edly takes  place  in  solutions  that  are  neutral.  So  far 
as  known,  ptyalin  is  formed  directly  by  the  cells,  and 
there  is  no  intermediate  stage  of  a  zymogen.  If  such  a 
substance  should  be  discovered,  it  would,  by  analogy,  be 
called  "  ptyalinogen."  Ptyalin  is  an  amylolytic  enzyme, 
but  acts  only  on  cooked  starch. 

Amylopsin. — This  substance  is  also  an  amylolytic  en- 
zyme, and  acts  on  both  cooked  and  raw  starch.  Its 
action  is  more  rapid  than  that  of  ptyalin,  and  further  it 


ENZYMES.  73 

changes  the  maltose  into  dextrose,  in  which  form  sugar 
is  absorbed  during  the  digestive  process. 

Pepsin. — This  substance  is  the  enzyme  of  the  gastric 
juice,  and  is  proteolytic  in  its  action.  There  exists  for 
pepsin  a  true  zymogen,  pepsinogen,  which  is  formed  by 
the  cells  of  the  gastric  glands,  and  under  the  influence 
of  the  hydrochloric  acid  of  the  gastric  juice  the  pepsin- 
ogen becomes  pepsin.  Pepsin  exerts  its  proteolytic  action 
only  in  the  presence  of  an  acid,  of  which,  for  experi- 
mental purposes,  hydrochloric  acid,  0.2  per  cent.,  is  the 
best. 

Trypsin. — This  substance  is  the  proteolytic  enzyme  of 
pancreatic  juice.  Considerable  study  has  been  made  of 
trypsin,  its  composition  being  given  as  follows  :  carbon, 
47.22  to  48.09 ;  hydrogen,  7.15  to  7.44;  nitrogen,  12.59 
to  13.41  ;  sulphur,  1.73  to  1.86.  Trypsin  acts  most 
promptly  in  the  presence  of  an  alkali,  but  it  will  act 
also  in  neutral  solutions  or  even  when  0.012  per  cent,  of 
hydrochloric  acid  is  present ;  but  its  action  ceases  when 
free  hydrochloric  acid  is  present  to  the  amount  of  o.  i  per 
cent. 

In  connection  with  this  enzyme  it  is  interesting  to 
note  that  the  contents  of  the  small  intestine,  into  which 
the  pancreatic  juice  is  discharged,  are  not  invariable  in 
their  reaction.  Sometimes  they  are  alkaline,  at  other  times 
neutral,  and  they  may  even  be  acid.  When  this  acidity 
exists  in  the  upper  part  of  the  small  intestine,  it  is  due 
to  the  hydrochloric  acid  produced  by  the  stomach,  but 
when  it  is  found  elsewhere  it  is  attributable  to  lactic  or 
butyric  acid  formed  as  a  result  of  fermentation  of  the 
carbohydrates  of  the  food.  It  is  claimed  that  a  small 
amount  of  lactic  acid,  less  than  0.05  per  cent.,  is  an  aid 
to  the  proteolytic  action  of  trypsin,  but  that  more  than 


74  HUMAN  PHYSIOLOGY. 

this  percentage  puts  a  stop  to  the  process.  Trypsin  has 
its  zymogen,  which  is  called  "  trypsinogen." 

Pialyn  (Steapsin). — This  enzyme  is  sometimes  spoken 
of  as  the  "  fat-splitting  ferment,"  because  its  action  is  to 
decompose  the  neutral  fats,  the  result  being  a  fatty  acid 
and  glycerin.  The  optimum  temperature  for  the  action 
of  pialyn  is  40°  C,  and  the  most  favorable  reaction  is  a 
slightly  alkaline  one. 

Rennin. — In  cheese-making  the  casein  of  milk  is  co- 
agulated by  rennet,  which  is  an  infusion  in  brine  of  the 
fourth  stomach  of  the  calf  This  coagulating  property 
of  rennet  is  due  to  an  enzyme  to  which  has  been  given 
the  names  of  "  rennet  ferment,"  "  milk-curdling  ferment," 
and  "  rennin."  Rennin  may  be  extracted  from  the  mucous 
membrane  of  the  stomach  of  most  animals,  including 
man.  The  zymogen  of  rennin  is  denominated  "  ren- 
ninogen." 

Fibrin-ferment. — The  clotting  of  blood  is  due  to  the 
change  of  its  fibrinogen  into  fibrin  under  the  influence 
of  an  enzyme,  fibrin-ferment.  The  theory  that  this  clot- 
ting is  produced  by  the  breaking  down  of  the  white  cor- 
puscles seems  to  be  the  most  reasonable  one  at  the  pres- 
ent time.  In  the  consideration  of  the  coagulation  of  the 
blood  this  subject  will  again  be  referred  to. 

Muscle-ensynie. — The  clotting  of  the  plasma  of  muscle 
is  attributed  to  this  enzyme,  which  is  regarded  as  dis- 
tinct from  fibrin-ferment.  It  is  sometimes  spoken  of  as 
"  myosin-ferment." 

G.  Intermediate  Products. 
There  exists  in  the  body  a  class  of  substances  which, 
after  they  are  formed  by  the  tissues,  perform  some  office  in 
the  economy  of  the  body,  but  what  this  office  is,  exactly, 


INTERMEDIATE   PRODUCTS.  75 

is  not  understood.  These  substances  are  not  permanent, 
but  undergo  changes  into  other  forms,  and  are  therefore 
known  as  "  intermediate  products  "  or  "  by-products." 

Sodium  GlycocJiolate  (CagH^jNOgNa)  is  one  of  the  in- 
gredients of  the  bile  of  man,  of  the  ox,  and  of  other 
animals,  only  traces  of  it  being  found  in  the  carnivora, 
some  authorities  claiming  it  to  be  absent.  This  salt  con- 
sists of  glycocholic  acid  united  with  sodium.  Glycocholic 
acid  is  composed  of  glycin  and  cholalic  acid,  and  is  some- 
times found  in  the  urine  in  jaundice. 

Sodium  Taurocliolate  {C26H45NS07Na)  and  sodium 
glycocholate  are  known  as  the  "  bile-salts."  Sodium 
taurocholate,  which  is  composed  of  taurocholic  acid  and 
sodium,  exists  in  both  human  and  ox  bile.  In  the  bile 
of  carnivora  it  exists  without  the  glycocholate.  Tauro- 
cholic acid  is  composed  of  taurin  and  cholalic  acid. 
Cholalic  acid  or  cholic  acid,  which  is  produced  by  the 
decomposition  of  the  bile-acids,  is  formed  in  the  small 
intestine,  and  still  more  abundantly  in  the  large  intestine. 
Taurocholic  acid  precipitates  ordinary  proteids  from  their 
solutions,  but  has  no  such  action  on  peptones.  When 
the  contents  of  the  stomach,  therefore,  enter  the  small 
intestine,  the  proteids  are  thrown  down  and  the  enzymes 
can  act  upon  them  more  readily,  while  the  peptones  are 
absorbed.  This  acid  is  said  also  to  possess  antiseptic 
properties  to  a  marked  degree. 

Petterikofer  s  Test  for  Bile-acids. — This  test  consists  in 
the  production  of  a  cherry-red  color,  which  changes  to  a 
purple,  when  a  few  drops  of  a  20  per  cent,  solution  of 
cane-sugar  are  added  to  a  solution  of  bile-acids  or  the 
biliary^  salts  and  followed  by  concentrated  sulphuric  acid. 
Other  substances,  such  as  morphine  and  salicylic  acid, 
will  give  the  same  color  reactions,  so  that  to  exclude  them 


'j6  HUMAN  PHYSIOLOGY. 

it  is  necessary  to  evaporate  to  dryness  the  fluid  to  be  ex- 
amined, to  extract  with  absolute  alcohol,  and  to  precip- 
itate by  the  addition  of  ether  in  excess.  To  this  precip- 
itate, when  dissolved  in  water,  the  test  may  be  applied  as 
already  indicated. 

Lecithin  (C44H9QNPO9). — This  ingredient  is  sometimes 
known  as  "  phosphorized  fat."  It  is  a  constituent  of  the 
red  and  white  blood-corpuscles,  of  the  bile,  brain,  nerves, 
semen,  and  pus.  It  occurs  also  in  yeast  and  in  other 
vegetable  cells,  in  the  yolk  of  ^^%,  and  in  milk. 

Cerebrin  (Cj^NggNOg). — This  substance  is  found  in  the 
brain,  in  nerves,  and  in  pus-corpuscles. 

Protagon  (CigoHgogNgPOgg). — This  substance  is  also 
found  in  the  brain.  It  is  still  undecided  whether  pro- 
tagon is  an  independent  substance  or  is  a  mixture  of 
lecithin  and  cerebrin,  although  evidence  is  accumulating 
which  indicates  that  it  is  not  a  mixture. 

H.  Waste  Products. 

This  class  includes  substances  which  are  the  result 
of  the  disintegrative  changes  that  occur  in  the  tissues  of 
the  body  and  in  the  food.  After  being  formed  they  are 
eliminated,  being  of  no  use. 

Krcatin  (QHgNgOg). — This  substance  is  one  of  the 
characteristic  ingredients  of  the  muscles,  and  in  the 
metabolism  of  these  tissues  ultimately  becomes  con- 
verted into  urea.  Kreatin  occurs  also  in  nervous  tissues. 
It  is  not  a  constituent  of  urine,  although  it  is  sometimes 
so  regarded.  When  found  in  this  fluid  it  has  doubtless 
been  produced  from  kreatinin  by  the  methods  used  to 
obtain  it  from  the  urine.  Kreatin  readily  becomes  con- 
verted into  kreatinin  by  giving  up  a  molecule  of  water. 

Kreatinin  (C^H^NgO). — A  comparison  of  the  formulae 


WASTE  PRODUCTS.  7/ 

of  kreatin  and  kreatinin  shows  that  the  latter  is  a  de- 
hydrated form  of  the  former.  Kreatinin  readily  unites 
with  water,  forming  kreatin ;  it  exists  in  the  urine  in  pro- 
portions which  vary  according  to  the  amount  of  proteids 
eaten — from  0.5  to  4.9  grammes  per  diem. 

Urea  ((NH2)2CO)  is  the  principal  waste  product  in  the 
urine  of  mammals,  although  it  occurs  in  small  amounts 
in  that  of  birds,  especially  when  they  are  fed  on  meat., 
In  the  urine  of  man  it  is  present  to  the  amount  of  2.5 
to  3.2  per  cent,  30  grammes  on  an  average  being  daily 
excreted.  In  blood  it  occurs  in  the  proportion  of  0.025 
per  cent.,  and  it  may  also  be  obtained  from  lymph,  per- 
spiration, and  from  the  liver.  Urea  is  soluble  in  water 
and  alcohol,  but  insoluble  in  anhydrous  ether.  Under 
the  influence  of  bacteria,  urea  undergoes  alkaline  fer- 
mentation, in  which  two  molecules  of  water  are  taken 
up  and  carbonate  of  ammonia  is  formed.  This  change  is 
expressed  by  the  formula 

(NH2)2CO  -f  2H2O  =  (NHJ^CO^ 

Urea.  Water.  Carbonate  of 

ammonia. 

The  source  of  urea  is  from  the  kreatin  of  muscular 
tissue,  and  the  liver  is,  in  all  probability,  the  organ  in 
which  take  place  the  transformations  that  result  in  its 
production,  so  that  when  this  organ  is  diseased  there  is 
likely  to  be  a  diminished  amount  of  urea  excreted. 

Uric  Acid  (C5H4N4O3)  is  found  in  small  quantities  in 
human  urine,  only  from  0.2  to  i  gramme  being  daily  ex- 
creted. This  acid  is,  however,  abundant  in  the  urine 
of  birds  and  of  reptiles.  It  is  found  constantly  in  the 
spleen,  and  it  has  been  found  also  in  the  lungs,  the  heart, 
the  pancreas,  the  brain,  and  the  liver.    The  calculi  which 


78  HUMAN  PHYSIOLOGY. 

form  in  the  urinary  organs  frequently  consist  of  uric  acid 
or  of  salts  formed  from  it.  The  so-called  "  concretions  " 
which  form  in  the  joints  of  persons  suffering  from  gout 
are  composed  of  uric  acid.  The  principal  salts  into  the 
formation  of  which  uric  acid  enters  are  sodium,  potas- 
sium, and  ammonium  urates.  In  the  production  of  urea 
uric  acid  is  regarded  as  one  of  the  steps. 

QH.NA  +  H,0  +  O  =  QH^NA  +  (NH2),CO 

Uric  acid.  Water.       Oxygen.  Alloxan.  Urea. 

Hippiiric  Acid  (C9H9NO3). — This  ingredient  of  human 
urine  is  excreted  to  the  amount  of  but  from  o.i  to  i.O 
gramme  per  diem.  It  is  much  more  abundant  in  horses 
and  in  other  herbivora. 

Leiicin  (C6Hm(NH2)O.OH)  occurs  in  the  pancreas, 
spleen,  thymus,  thyroid,  salivary  glands,  and  liver.  It 
is  sometimes  found  in  urine,  especially  in  certain  diseases 
of  the  liver,  such  as  acute  yellow  atrophy.  Leucin  occurs 
also  in  the  bulbs,  tubers,  and  seeds  of  some  plants.  It 
is  found  in  the  small  intestine  during  the  digestion  of 
proteids. 

Tyrosin  (CgHj^NOg). — This  is  an  ingredient  of  the  pan- 
creas and  pancreatic  juice  and  of  the  .spleen.  Tyrosin  is 
intimately  associated  with  leucin,  being  found  with  it  dur- 
ing the  pancreatic  digestion  of  proteids ;  also  in  urine 
during  diseases  of  the  liver,  and  in  plants. 

Indol  (CgH^N)  occurs  in  the  faeces,  and  is  one  of  the 
ingredients  which  gives  them  their  peculiar  odor.  Indol 
is  a  product  of  the  decomposition  of  proteids  which 
occurs  in  the  intestines. 

Skatol  (C9H9N)  occurs  in  the  faeces  with  indol,  and  it 
contributes  to  produce  the  faecal  odor. 


COL  O  RING-MA  TTERS.  79 


I.  Coloring-matters. 


HcBmoglobin  (Reduced  Haemoglobin)  (CgugHggoNjj^FeSj- 
O179). — Haemoglobin  with  oxyhaemoglobin  gives  the 
characteristic  color  to  the  bipod.  In  the  blood  of  an 
asphyxiated  animal  the  coloring-matter  is  almost  entirely 
haemoglobin  ;  in  venous  b-lood  it  is  both  haemoglobin  and 
oxyhaemoglobin,  while  in  arterial  blood  the  oxyhaemo- 
globin is  in  excess.  It  is  probable  that  there  are  various 
haemoglobins,  as  this  ingredient  obtained  from  the  blood 
of  different  animals  varies  in  important  particulars.  The 
percentage  composition  of  that  of  the  dog  is  as  follows  : 
carbon,  53.85  ;  hydrogen,  7.32  ;  nitrogen,  16.17;  sulphur, 
0.390;  iron,  0.430  ;  oxygen,  21.84.  The  great  physio- 
logical interest  which  attaches  to  this  substance  is  due 
to  its  affinity  for,  and  the  readiness  with  which  it  gives 
up,  oxygen. 

Oxyhcemoglobin  is  a  compound  of  one  molecule  of 
oxygen  and  one  molecule  of  haemoglobin.  The  power 
of  haemoglobin  to  take  up  oxygen  depends  upon  the  iron 
it  contains.  When  oxyhaemoglobin  is  treated  with  acids 
or  with  strong  alkalies  it  is  decomposed,  the  products 
being  a  proteid,  globin,  and  haematin.  This  change 
takes  place  in  extravasated  blood  and  also  during  diges- 
tion. Haematin  may  be  found  in  the  faeces,  especially 
after  a  meat  diet.  If  to  dried  blood  a  crystal  of  common 
salt  be  added,  and  on  this  be  dropped  glacial  acetic  acid, 
and  heat  be  then  applied,  there  form  crystals  which  are 
called  "  haemin  crystals."  Chemically  speaking,  they 
are  chloride  of  haematin. 

Carbon-monoxide  Hcsmoglobin. — A  union  of  one  mole- 
cule of  haemoglobin  and  one  of  carbon  monoxide  pro- 
duces the  coloring-matter  carbon-monoxide  haemoglobin. 


8o  HUMAN  PHYSIOLOGY. 

If  a  current  of  carbon  monoxide  be  passed  through  a  so- 
lution of  oxyhaemoglobin,  the  gas  will  displace  the  oxy- 
gen and  carbon-monoxide  haemoglobin  will  be  formed. 
An  important  difference  is  to  be  noted  in  the  behavior 
of  this  gas  as  compared  with  oxygen :  while  oxygen  is 
easily  replaced,  carbon  monoxide  is  not.  Carbon  mon- 
oxide is  the  gas  formed  when  combustion  is  incomplete, 
such  as  is  produced  by  the  charcoal  furnace  used  in 
France  for  suicidal  purposes  ;  the  charcoal  fumes  when 
inhaled  in  sufficient  quantity  produce  fatal  results.  The 
combinations  of  haemoglobin  with  oxygen,  carbon  mon- 
oxide, and  other  gases  are  definite  compounds,  each  of 
which  crystallizes  in  its  own  characteristic  form  and  has 
its  own  spectrum. 

Bilirubin  (C16HJ8N2O3). — The  bile  of  man  and  of 
carnivora  owes  its '  golden-red  color  to  bilirubin.  This 
coloring-matter  is  insoluble  in  water,  but  is  very  soluble 
in  solutions  that  are  alkaline.  Bilirubin  is  identical  with 
what  was  formerly  called  "  haematoidin,"  a  coloring-mat- 
ter found  in  old  blood-clots,  in  corpora  lutea,  and  some- 
times in  urine. 

Biliverdin  (CigHigNjOJ,  which  is  the  coloring-matter 
of  the  bile  of  herbivora,  is  characterized  by  its  bright- 
green  color.  Its  formula  shows  that  it  is  oxidized  bili- 
rubin, and  when  the  golden-red  bile  of  carnivora  is  ex- 
posed to  the  air  it  becomes  green,  its  bilirubin  having 
been  changed  into  biliverdin.  Any  oxidizing  agent  pro- 
duces the  same  effect,  and  on  this  fact  are  based  tests 
for  the  presence  of  the  bile-pigment.  Gmelin's  test  is 
as  follows  :  Nitric  acid,  which  contains  nitrous  acid,  is 
poured  into  a  test-tube,  and  upon  it  is  poured  the  fluid  sus- 
pected of  containing  the  coloring-matter,  care  being  taken 
.not  to  mix  the  two,  but  to  permit  the  fluid  to  float  on  the 


COL  ORING-  MA  TTERS.  8 1 

acid.  If  the  bile-pigments  be  present,  colored  rings 
appear  where  the  two  fluids  join,  the  ring  nearest  the 
acid  being  yellow,  and  those  above  being  red,  violet, 
blue,  and  green.  This  test  is  sufficiently  delicate  to 
detect  the  presence  of  i  part  of  bilirubin  in  70,000  parts 
of  the  solvent. 

Hydrobilirubin  {Q^^^f^^  is  another  coloring-matter 
in  the  bile,  and  exists  also  in  faeces,  in  which  it  has  been 
described  as  "  stercobilin."  The  identity  of  hydrobili- 
rubin and  urobilin,  a  coloring-matter  of  the  urine,  may 
now  be  regarded  as  established.  It  gives  to  the  urine  a 
red  or  reddish-yellow  color,  and  is  especially  abundant 
in  highly-colored  urine,  as  in  fevers.  One  authority  at 
least  believes  that  the  urobilin  of  normal  urine  and  that 
of  pathological  urine  have  certain  essential  points  of 
difference. 

All  these  bile-pigments  are  regarded  as  being  derived 
from  haemoglobin,  and  the  liver-cells  are  probably  the 
structures  endowed  with  the  power  of  their  formation. 

Urochrome. — This  coloring-matter  of  the  urine  is  re- 
garded by  some  as  distinct  from,  and  by  others  as  iden- 
tical with,  urobilin. 

Melanins. — There  is  a  group  of  substances  to  which 
the  name  melanins  might  well  be  given,  as  its  members 
differ  somewhat  from  one  another.  In  general  this  group 
comprises  the  black  or  dark  pigments,  as  in  the  choroid, 
the  skin,  etc. 

Fiiscin  is  the  melanin  of  the  cell-substance  and  pro- 
cesses of  the  retinal  epithelium. 

Urinary  melanin  is  the  name  given  to  the  coloring- 
matter  of  the  dark-brown  or  black  urine  of  persons 
suffering  with  melanotic  tumors ;  that  is,  tumors  which 
are  dark-colored  from  containing-  a  melanin. 


82  HUMAN  PHYSIOLOGY. 

Lutein  is  the  yellow  pigment  of  the  corpus  luteum. 
Serum-lutein  is  the  pigment  which  gives  the  yellowish 
color  to  the  serum  of  blood.  This  fluid  may  sometimes 
owe  part  of  its  color  to  bile-pigments. 


FOOD. 


The  human  body  is  constantly  wasting.  In  a  single 
day  this  waste  is  estimated  to  be  at  least  eight  pounds. 
If  this  loss  were  not  compensated  for,  death  would  result 
from  starvation,  the  length  of  time  necessary  to  produce 
this  fatal  result  depending  much  on  circumstances.  In 
one  instance,  in  which  one  hundred  and  fifty  persons 
in  1816  were  wrecked  on  the  "Medusa,"  after  being 
thirteen  days  without  food  either  solid  or  liquid  all  were 
dead  but  fifteen.  It  is,  however,  to  be  said  that  in  this 
case  there  was  not  only  absence  of  food,  but  as  an  addi- 
tional factor  in  hastening  the  result  there  was  also  ex- 
posure to  the  elements.  It  may  be  said,  in  general,  that 
death  will  supervene  when  the  body  has  lost  four-tenths 
of  its  weight.  To  supply  the  waste  of  the  body  and  to 
maintain  it  in  its  physiological  condition  food  is  taken. 

There  is  a  process  of  oxidation  taking  place  in  the 
body  in  which  the  oxygen  taken  in  by  the  lung  oxidizes 
some  of  the  fats,  carbohydrates,  and  proteids,  and  as  a 
result  there  are  formed  carbon  dioxide,  water,  and  urea; 
that  is,  complex  substances  are  broken  up  into  simpler 
forms  and  energy  is  produced.  Besides  this,  the  body 
is  constantly  the  seat  of  certain  activities,  as  movements 
of  the  muscles,  the  production  of  vital  heat,  and  nervous 
activity,  and  for  this  food  is  also  required.  Food,  tJien, 
may  be  defined  as  material  taken  into  the  body  to  repair 


FOOD.  83 

the  zvaste  of  tissues  and  to  produce  energy.  Foods  are 
made  up  of  food-stuffs  and  otlier  substances  associated 
with  them,  which  latter,  being  indigestible,  are  of  no 
value  either  for  purposes  of  nutrition  or  for  the  genera- 
tion of  energy. 

Foodstuffs  are  divided  into  four  classes,  and  they  have 
already  been  discussed  in  treating  of  the  physiological 
ingredients.     The  classes  of  food-stuffs  are : 

1.  Inorganic,  including  water  and  salts. 

2.  Carbohydrates. 

3.  Fats  or  oils. 

4.  Proteids. 

I.  Inorganic  Food-stuffs. —  Water  is,  as  has  been 
pointed  out,  one  of  the  most  important  ingredients  of  the 
body,  and  is  therefore  one  of  the  most  essential  of  the  food- 
stuffs. It  is  the  solvent  of  many  of  the  constituents  of 
the  food  and  the  salts,  and  by  its  softening  action  on  the 
dry  parts  aids  in  the  processes  by  which  they  are  masti- 
cated and  swallowed.  It  is  important  to  remember  that 
water  should  be  free  from  such  impurities  as  render  it 
harmful.  Thus,  if  it  be  too  "  hard  " — that  is,  contains 
too  much  lime — there  is  liability  to  the  production  of 
gastric  or  intestinal  derangements  ;  if  it  contain  the 
germs  of  disease,  sickness  may  follow  its  use.  It  is  by 
drinking  water  infected  with  the  germs  of  cholera  or  of 
typhoid  fever  that  these  diseases  are  often  produced.  To 
avoid  this  danger,  when  there  is  any  doubt  as  to  the 
purity  of  the  water  it  should  be  boiled.  In  one  family 
known  to  the  writer  no  water  that  has  not  been  boiled 
has  been  drunk  for  many  months. 

The  impression  that  boiled  water  is  unpalatable  is 
erroneous.  But  boiling  the  water  will  be  of  no  avail 
in  avoiding  the  danger  of  infection  if  impure  ice  be  used 


84  HUMAN  PHYSIOLOGY. 

in  connection  with  it.  Nothing  is  more  clearly  settled 
than  that  freezing  does  not  destroy  all  disease-producing 
germs.  The  typhoid-fever  epidemic  which  occurred  in 
1885  at  Plymouth,  Pa.,  where,  of  a  population  of  8000, 
1 153  persons  were  stricken  with  the  disease,  1 14  of  them 
dying,  is  a  striking  instance  of  the  vitality  of  the  typhoid 
germs.  The  drinking-water  of  Plymouth  became  con- 
taminated from  the  faeces  of  a  patient  having  typhoid 
fever,  although  these  faeces  had  been  frozen  for  a  long 
time  during  the  winter  months.  Laboratory  experiments 
have  demonstrated  that  the  germs  of  this  disease  may 
be  frozen  for  more  than  one  hundred  days  and  still  retain 
their  vitality. 

The  writer  investigated  an  epidemic  of  dysentery  in 
which  the  disease  was  traced  to  ice  used  in  drinking- 
water.  The  ice  had  been  cut  from  a  pond  in  which 
during  the  summer  hogs  wallowed,  and  in  which  they 
deposited  their  excreta.  When  melted  this  ice  had  a 
most  offensive  odor.  Other  instances  might  be  given  show- 
ing the  danger  from  the  use  of  impure  ice,  but  the  one 
cited  will  suffice.  Fortunately,  there  is  now  furnished  for 
use  in  many  of  our  cities  artificial  ice,  which,  if  properly 
prepared,  is  free  from  all  contamination.  In  this  process 
of  manufacturing  ice  the  water  is  not  only  boiled,  but  is 
distilled,  and  when  ready  for  freezing  is  absolutely  pure. 
With  boiled  water  and  artificial  ice  all  danger  of  infection 
through  these  channels  may  surely  be  prevented. 

Salts. — The  list  of  salts  taken  in  with  the  food  has 
already  been  given,  the  most  important  being  sodium 
chloride,  calcium  phosphate,  and  the  alkaline  carbonates 
and  phosphates.  The  offices  which  these  salts  perform 
in  the  economy  of  the  body  vary.  By  some  of  them 
the  solubility  of  certain  ingredients  is  made  possible,  as 


FOOD.  85 

is  the  globulin  in  the  blood  by  virtue  of  the  presence  of 
sodium  chloride.  Salts  are  stimulants  also  to  the  glands, 
causing  the  latter  to  secrete  more  actively ;  thus  the  di- 
gestive fluids  are  more  abundantly  poured  out  when  the 
food  is  properly;salted,  and  the  kidneys  more  completely 
perform  their  functions  under  the  stimulation  of  the 
salts. 

2.  Carbohydrates. — These  food-stuffs,  in  the  form 
of  starch  and  sugar,  are  especially  abundant  in  vegetable 
foods  and  in  milk,  and  less  so  in  animal  foods. 

3.  Fats  or  Oils. — These  food-stuffs  are  found  in  milk, 
in  butter,  in  cheese,  in  the  fatty  tissues  of  meat,  and  also 
in  some  vegetables,  such  as  nuts.  The  following  table 
shows  the  amount  in  some  of  the  ordinary  foods : 

Meat 5  to  10  per  cent. 

Milk 3  to    4     " 

Eggs 12 

Cheese 8  to  30     " 

Butter 85  to  90     "       " 

4.  Pkoteids. — This  class  contains  some  of  the  most 
valuable  of  the  food-stuffs.  The  importance  of  this 
cla.ss  is  readily  under.stood  when  it  is  recalled  that  the 
principal  ingredients  of  the  blood  and  the  muscles  are 
supplied  by  the  protcids  of  the  food.  This  is  the  only 
class  who.se  members  contain  nitrogen,  and  it  has  there- 
fore been  sometimes  .spoken  of  as  the  "  nitrogenous  ' 
class.  The  albuminoids  contain  nitrogen  also,  but  this 
class  has  little  nutritive  value,  except  gelatin,  which 
is  valuable,  but,  as  has  already  been  .stated,  its  nitro- 
gen is  not  available  for  the  tissues.  The  proteids  are 
represented   in  eggs   by  albumin,  in  milk  by  casein,  in 


86 


HUMA  N  PH  YSIOL  O  G  Y. 


meat  by  myosin,  in  peas  and  in  beans  by  legumin,  and 
in  the  cereals  by  gluten.  The  amount  of  proteids  varies 
in  different  foods ;  thus  there  is  in 


Meat  .... 
Milk  .... 
Peas  and  beans 
Grains  (flour) 
Bread  .  .  . 
Potatoes      .    . 


15  to  23  per  cent. 

3  to    4  " 

23  to  27  " 

8  to  II  " 

6  to    9  " 

I  to    4  " 


The  following  diagram  (Fig.  4)  shows  the  amount  of 
the  principal  food-stuffs  in  some  of  the  more  generally 
used  foods : 

Proteids.  Fats.  Carbohydrates.  Water. 


Explanation. 


Human  milk 


Cow's  milk , 


m    6 

87i, 

1 

slllllllllll^M 

— 'SS=^SrE^=?^=^S=:=^==2=£:3:^ 

^^^^^^^^^i^ 

3t 

■?-Ni 

86 

■ 

;illll^sfl 

e==^==^eSSe=^SS5S 

=-^.^£r=£r^=:?^:Z=^?5^ 

Fish... 


Leguminous  fruits. 


Potatoes 


7 fig 


15 


20l 


2j5 ae 


6  i 


5S 


S6 


Bread | 

Fig.  4. — Diagram  showing  the  proportion  of  the  principal  food-stuffs  in  a  few  typical 

comestibles.     Tlie  numbers  indicate  percentages.     Salts  and  indigestible  materials 

omitted.     (After  Yeo.) 

From  the  above  consideration  of  the  food-stuffs  it  is 
seen  that  they  are  in  most  respects  the  same  as  the  tis- 


FOOD.  87 

sues  of  the  body  ;  yet  it  would  be  erroneous  to  infer  that 
the  fats  and  the  proteids  of  the  food  go  directly  into  the 
tissues  as  such,  and  take  the  place  of  the  fats  and  proteids 
which  are  wasted.  There  are  many  intermediate  steps, 
some  of  which  are  known  and  will  be  discussed,  and 
others  of  which  we  are  entirely  ignorant.  Experience 
has  abundantly  demonstrated  that  in  order  to  maintain 
the  body  at  its  physiological  standard,  representatives 
from  all  these  four  classes  of  food-stuffs  must  be  sup- 
plied. If  man  be  deprived  of  water,  death  speedily  re- 
sults ;  it  comes  as  surely,  though  not  so  quickly,  if  fats 
or  carbohydrates  or  proteids  be  cut  off  from  the  food- 
supply.  Indeed,  a  man  may  be  starved  to  death  by  with- 
holding the  salts. 

Whenever,  therefore,  it  is  found  that  life  can  be  main- 
tained physiologically  for  a  long  period  of  time  on  any 
diet,  it  is  certain  that  this  diet  contains  representatives 
of  all  the  classes  enumerated.  Thus,  milk,  which  is  the 
sole  food  of  young  children — among  some  of  the  Eskimos 
to  the  sixth  year  of  life — is  found  on  analysis  to  con- 
tain such  representatives,  the  inorganic  class  being  rep- 
resented by  water  and  salts,  the  carbohydrates  by  milk- 
sugar,  the  fats  by  butter,  and  the  proteids  by  casein 
and  some  albumin.  It  is  not,  howev^er,  sufficient  that 
each  class  should  be  represented,  but  the  proportions 
of  the  ingredients  must  be  proper.  It  is  possible  that 
any  given  food  may  have  the  requisite  constituents,  but 
may  have  too  much  of  one  and  too  little  of  another. 
It  has  been  determined  that  the  daily  waste  of  the  body 
is  4500  grains  of  carbon  and  300  grains  of  nitrogen,  or 
15  to  I,  so  that  in  the  food  the  nitrogen  should  be  to  the 
carbon  as  i  is  to  15. 

In  the  table  given  above  it  is  seen  that  in  the  proteids 


88  HUMAN  PHYSIOLOGY. 

there  are  three  times  as  much  carbon  as  nitrogen,  so  that 
should  proteids  only  be  supplied  to  the  body  there  would 
have  to  be  given  an  enormous  amount  of  nitrogenous 
food  in  order  to  supply  enough  of  the  carbonaceous. 
The  effect  of  this  excess  of  nitrogenous  food  would  be 
to  injure  the  digestive  and  eliminating  organs.  Imag- 
ine, for  instance,  the  effect  upon  the  digestive  apparatus 
if  man's  exclusive  diet  were  potatoes.  It  will  be  seen 
by  the  table  that  in  potatoes  there  are  2  per  cent,  of 
proteids  and  20.75  P^^  cent,  of  carbohydrates.  There- 
fore, to  obtain  enough  proteids  from  potatoes  to  sustain 
life  it  would  be  necessary  to  eat  daily  at  least  ten  pounds, 
or  thirty  good-sized  potatoes.  In  some  parts  of  the 
world  this  has  been  put  into  practice,  the  effect  being  to 
distend  the  stomach  and  to  derange  digestion  to  a  harm- 
ful degree. 

If  the  diet  were  exclusively  of  meat,  then  in  order  to 
supply  the  body  with  the  necessary  amount  of  car- 
bonaceous material  a  very  large  quantity  of  meat  would 
be  required,  and  to  meet  this  requirement  there  would 
be  taken  in  an  excess  of  nitrogenous  constituents,  thus 
placing  a  serious  burden  on  the  eliminating  organs  to 
get  rid  of  them.  Experience  demonstrates  that  a  mix- 
ture of  foods  is  the  true  physiological  method  of  supply- 
ing the  wants  of  the  human  body:  from  meat  is  obtained 
the  proteids  necessary  for  nutrition  ;  from  the  potato  is 
derived  the  starch  ;  and  from  butter  is  secured  the  fat. 
Experience  shows  also  that  a  higher  standard  of  effi- 
ciency is  maintained  by  a  variety  of  food,  a  change  being 
made  from  one  kind  of  meat  to  another  and  from  one 
vegetable  to  another,  always,  however,  giving  the  body 
the  food-stuffs  in  the  proper  quantities  to  supply  its 
demands. 


FOOD.  89 

There  are  individuals  who  believe  that  meat-eating  is 
not  only  unnecessary  to,  but  that  it  tends  also  to  degrade, 
man  ;  they  consequently  confine  themselves  to  vegetable 
diet :  this  exclusive  dietary  practice  is  called  "  vegeta- 
rianism." It  is  true  that  vegetables  contain  all  the  phys- 
iological ingredients  necessary  for  nutrition,  but,  as  above 
noted  in  the  case  of  potatoes,  the  proportion  is  not  such 
as  will  subserve  the  best  interests  of  the  body,  and  phys- 
iologists have  decried  the  system  as  being  irrational. 
The  following  extract  from  a  letter  of  Dr.  Alanus,  a  veg- 
etarian, published  in  the  Medical  and  Surgical  Reporter, 
gives  his  experience  in  this  matter : 

"  Having  lived  for  a  long  time  as  a  vegetarian  without 
feeling  any  better  or  worse  than  formerly  with  mixed 
food,  I  made  one  day  the  disagreeable  discovery  that  my 
arteries  began  to  show  signs  of  atheromatous  degenera- 
tion. Particularly  in  the  temporal  and  radial  arteries 
this  morbid  process  was  unmistakable.  Being  still  under 
forty,  I  could  not  interpret  this  symptom  as  a  manifesta- 
tion of  old  age,  and  being,  furthermore,  not  addicted  to 
drink,  I  was  utterly  unable  to  explain  the  matter.  I 
turned  it  over  and  over  in  my  mind  without  finding  a 
solution  of  the  enigma.  I,  however,  found  the  explana- 
tion quite  accidentally  in  a  work  of  that  excellent  ph}-- 
sician.  Dr.  E.  Monin  of  Paris.  The  following  is  the 
verbal  translation  of  the  passage  in  question  :  '  In  order 
to  continue  the  criticism  of  vegetarianism  we  must  not 
ignore  the  work  of  the  late  lamented  Gubler  on  the  in- 
fluence, of  a  vegetable  diet  on  the  chalky  degeneration 
of  the  arteries.  Vegetable  food,  richer  in  mineral  salts 
than  that  of  animal  origin,  introduces  more  mineral  salts 
into  the  blood.  Raymond  has  observed  numerous  cases 
of  atheroma  in  a  monastery  of  vegetarian  friars,  amongst 


90  HUMAN  PHYSIOLOGY. 

Others  that  of  the  prior,  a  man  scarcely  thirty-two  years 
old,  whose  arteries  were  already  considerably  indurated. 
The  naval  surgeon,  Treille,  has  seen  numerous  cases  of 
atheromatous  degeneration  in  Bombay  and  Calcutta, 
where  many  people  live  exclusively  on  rice.  A  vegeta- 
ble diet,  therefore,  ruins  the  blood-vessels  and  makes  one 
prematurely  old,  if  it  is  true  that  a  man  is  as  old  as  his 
arteries.  It  must  produce  at  the  same  time  tartar,  the 
senile  arch  of  the  cornea,  and  phosphaturia.'  Having, 
unfortunately,  seen  these  newest  results  of  medical  in- 
vestigation confirmed  by  my  own  case,  I  have,  as  a 
matter  of  course,  returned  to  a  mixed  diet.  I  can  no 
longer  consider  purely  vegetable  food  as  the  normal  diet 
of  man,  but  only  as  a  curative  method  which  is  of  the 
greatest  service  in  various  morbid  states.  Some  patients 
may  follow  this  diet  for  weeks  and  months,  but  it  is  not 
adapted  for  everybody's  continued  use.  It  is  the  same 
as  with  the  starvation  cure,  which  cures  some  patients, 
but  is  not  fit  to  be  used  continually  by  the  healthy.  I 
have  become  richer  by  one  experience,  which  has  shown 
me  that  a  single  brutal  fact  can  knock  down  the  most 
beautiful  theoretical  structure." 

Another  factor  to  determine  the  nutritive  value  of  any 
food  is  its  digestibility.  The  chemical  analysis  of  cheese 
would  place  it  high  among  the  foods,  but  experience 
shows  that  its  constitution  is  such  as  not  readily  to  per- 
mit the  action  of  the  digestive  fluids,  and  its  availability 
as  a  food  is  therefore  low. 

In  regard  to  meats,  it  may  be  said  that  veal  is  not  of 
such  nutritive  value  as  beef  Indeed,  to  many  persons 
it  seems  almost  poisonous.  It  is  certainly  much  less 
digestible  than  beef  or  mutton,  though  more  digestible 
when  roasted. 


FOOD.  91 

In   conclusion,  then,  the  following  table   is  given  as 
showing  a  simple  daily  diet  for  an  adult : 

Butter  or  fat 100  grammes. 

Meat 453 

Bread 540 

Water 1530         " 

With  this  diet  life  could  doubtless  be  maintained  for  a 
long  time,  but  for  reasons  already  given  it  should  be 
varied. 


II.  NUTRITIVE   FUNCTIONS. 
I.  Digestion. 

Having  considered  the  composition  of  the  body  and 
food,  there  may  now  be  taken  up  the  study  of  the  nutri- 
tive functions. 

As  has  already  been  noted,  the  body  is  constantly  pro- 
ducing energy  and  undergoing  ivaste,  both  of  which  re- 
quire the  taking  of  food.  But  food  is  absolutely  of  no 
use  to  the  body  until  it  reaches  the  blood  and  by  this 
fluid  is  conveyed  to  the  tissues.  So  long  as  the  food  re- 
mains within  the  alimentary  canal  it  is  as  much  outside 
the  body,  so  far  as  nutrition  is  concerned,  as  if  it  had 
never  been  taken  inside.  To  be  of  any  service  the  food 
must  enter  the  blood,  and  it  does  this  by  being  absorbed. 

In  some  forms  of  animal  life  the  food  is  of  such  a 
nature  that  it  readily  and  without  further  change  under- 
goes absorption  ;  that  is,  passes  through  the  walls  of  the 
absorbing  vessels.  In  other  forms  of  animal  life  this  is 
not  the  case :  in  the  latter  form  of  animals,  unless  cer- 
tain changes  take  place,  the  food  passes  out  of  the  ali- 
mentary canal  as  waste  material,  without  having  con- 
tributed to  the  nutrition  of  the  body  in  the  slightest 
degree.  Unless,  therefore,  some  provision  were  made 
to  obviate  this,  such  animals  would  die  of  starvation. 
The  provision  which  has  been  made  consists  in  the 
presence  of  certain  organs  whose  duty  is  to  change 
the  form  of  the  food-substances  from  that  in  which  they 
will  not,  into  that  in  which  they  will,  be  absorbed.  Sub- 
stances that  are  not  in  a  condition  to  be  absorbed — that 
is,  will  not  pass  through  animal  membranes — are  said  to 
be  "  non-diffusible ;"  those  that  are  in  a  condition  to  pass 

92 


DIGESTION. 


93 


through  are  said  to  be  "  diffusible."  The  above  change, 
then,  consists  mainly  in  the  alteration  from  a  non-diffusi- 
ble to  a  diffusible  state.  The  only  exception  to  this  rule 
is  that  of  the  fats,  which  are  otherwise  prepared.  It  is 
this  change  (its  preparation  for  absorption)  which  con- 
stitutes food-digestion,  and  the  organs  concerned  in 
bringing  about  these  necessary  changes  in  the  food 
are  the  digestive  organs. 

Manifestly,  these  organs  will  be  simple  or  be  complex 
according  to  the  amount  of  change  which  it  is  necessary 
to  bring  about  in  the  food  in  order  that  absorption  may 
take  place.  Thus,  if  the  food 
on  which  an  animal  relies  for 
its  sustentation  be  already  in 
a  diffusible  form,  no  change 
will  be  needed,  and  the  ani- 
mal will  therefore  have  no 
digestive  organs.  If  the  req- 
uisite change  be  a  slight  one, 
the  number  of  the  digestive 
organs  will  be  few  and  their 
structure  will  be  simple.  But 
if  the  food  be  varied  in  its 
composition,  and  largely 
made  up  of  non-diffusible 
food-stuffs,  then  the  digestive 
apparatu.s — that  is,  the  group 
of  organs  concerned  in  diges- 
tion— will  be  complex.  Such 
is  the  character  of  the  food 
of  man,  and,  consequently,  p,j, 
such  is  the  character  of  his 
digestive  apparatus  (Fig.  5). 


5. — I.  Stomach;  2-4.  Small  intes- 
tine :  5.  Caecum  :  6  Vermiform  ap- 
pendix ;  7,  8,  9.  Colon  ;  10.  Sigmoid 
flexure;   11.  Rectum;  12.  Spleen. 


94  HUMAN  PHYSIOLOGY. 

The  human  digestive  apparatus  consists  of  the  ali- 
mentary canal  and  the  other  digestive  organs,  which, 
although  outside,  still  communicate  with  this  canal  by- 
ducts  through  which  their  secretion  is  poured.  The  ali- 
mentary canal  consists  of  the  mouth,  the  oesophagus, 
the  stomach,  and  the  small  intestine.  The  digestive 
organs  which  are  outside,  but  discharge  their  secretion 
into,  this  canal  are  the  salivary  glands,  the  liver,  and  the 
pancreas. 

The  digestive  process  is  subdivided  into  three  parts  : 
(A)  That  which  takes  place  in  the  mouth  —  mouth 
digestion ;  (B)  that  which  takes  place  in  the  stomach — 
stomach  or  gastric  digestion ;  and  (C)  that  which  takes 
place  in  the  small  intestine — intestinal  digestion.  For- 
merly, when  digestion  was  spoken  of  it  was  always 
stomach  digestion  which  was  referred  to,  because  it 
was  supposed  that  the  entire  process  took  place  in 
that  organ,  and  when  digestion  was  impaired  the  rem- 
edies which  physicians  employed  were  directed  to  the 
stomach  alone.  There  is,  unfortunately,  too  much  of 
this  kind  of  practice  even  now,  but  the  study  of  phys- 
iology has  taught  that  indigestion  may  be  due  quite  as 
much  to  the  improper  performance  of  mouth  and  intestinal 
digestion  as  to  that  which  takes  place  in  the  stomach, 
and  unless  this  be  recognized  many  cases  will  unsuccess- 
fully be  treated. 

When  food  is  taken  into  the  mouth  it  has,  presumably, 
been  as  fully  prepared  as  possible  by  the  removal  of 
those  portions  which  are  of  no  nutritive  value.  No  one 
eats  the  husks  of  corn,  the  shells  of  nuts,  the  gristle  of 
meat,  or  similar  substances,  because  experience  has  shown 
that  they  are  of  little  or  of  no  nutritive  value  and  that  their 
digestion   is   practically  impossible.      Such  extraneous 


MOUTH  DIGESTION.  95 

matters,  therefore,  are  removed,  and  the  food  is  further 
prepared,  provided  this  preparation  be  necessary,  by  the 
process  of  cooking.  In  the  form,  then,  in  which  the 
food  is  taken  in  it  is  as  fully  prepared  as  it  can  be  out- 
side the  body.  Whatever  remains  to  be  done  in  order 
that  the  food  may  be  prepared  for  absorption  must  be 
effected  after  it  enters  the  alimentary  canal. 

Some  of  the  ingredients  of  human  food  are  already  in 
a  diffusible  form — that  is,  in  a  condition  to  be  absorbed 
by  the  blood-vessels  of  the  alimentary  canal — and  there- 
fore they  need  to  undergo  no  change.  Such  ingredients 
are  water,  salts,  and  dextrose,  and  were  they  the  only 
constituents  of  the  food,  no  digestive  organs  would  be 
needed ;  but,  as  already  seen,  this  is  not  the  fact.  The 
greater  part  of  the  food  is  in  a  non-diffusible  form,  and 
must  be  converted  into  a  diffusible  form  before  it  can 
be  absorbed.  The  first  step  in  this  conversion  is  that 
which  takes  place  in  the  mouth. 

A.  Mouth  Digestion. 

When  food  enters  the  mouth  it  consists  of  a  mixture 
of  various  food-stuffs.  In  order  that  the  changes  which 
these  food-.stuffs  undergo  may  be  traced  thoroughly,  let 
it  be  supposed  that  representatives  of  all  classes  of  food- 
stuffs are  present — namely,  (i)  inorganic,  salts  and  water; 
(2)  carbohydrates,  starch  and  sugar;  {■^)fats,  or  oils;  and 
(4)  proteids. 

The  water  and  salts  are  absorbed  directly  by  the  blood, 
for  the  most  part  from  the  stomach,  although  there  is 
doubtless  some  absorption  in  the  mouth.  If  the  food 
remained  in  the  mouth  a  longer  time  than  it  usually 
docs,  more  of  these  ingredients  would  there  be  absorbed, 
but  the  duration  of  time  is  so  short  that  the  amount  ab- 


96  HUMAN  PHYSIOLOGY. 

sorbed  cannot  be  very  great.  All  the  food  of  a  fluid 
nature,  no  matter  what  classes  of  food-stuffs  it  comprises, 
passes  immediately  from  the  mouth  into  the  pharynx, 
and  thence  through  the  oesophagus  into  the  stomach. 
Such  food  undergoes  no  chemical  changes  whatever  dur- 
ing this  time ;  thus,  milk,  chocolate,  and  beverages  of 
various  kinds  are  unchanged  in  this  part  of  digestion.  If, 
however,  fluids  be  taken  into  the  mouth  when  it  contains 
solid  food,  the  latter  will  be  softened  by  them,  and  the 
two  will  be  mixed,  and  will  come  under  the  influence  of 
the  agents  concerned  in  carrying  on  mouth  digestion. 
These  agents  are  the  teeth  and  the  salivary  glands. 

Mastication. — The  chewing  of  the  food,  or  mastication, 
is  performed  by  the  teeth,  of  which  there  are  two  sets. 
The  first  set  of  teeth,  which  are  known  as  "  temporary," 
"  deciduous,"  or  "  milk-teeth,"  and  which  exist  during 
early  childhood,  are  twenty  in  number,  and  the  second  or 
permanent  set,  which  begin  to  take  the  place  of  the  first 
set  at  about  the  sixth  year  of  life,  remain  to  a  greater  or 
lesser  extent  until  old  age.  The  latter  set  is  composed 
of  thirty- two  teeth — four  incisors,  two  canines,  four  bicus- 
pids, and  six  molars — in  each  jaw.  The  incisors,  or 
cutting  teeth,  are  adapted  to  bite  the  food ;  the  molar 
teeth,  or  grinders,  are  adapted  to  grind  the  food,  while  the 
canines  and  bicuspids  in  man  aid  the  incisors  and  molars. 
In  the  carnivora,  the  canines — or  "  tushes  "  as  they  are 
called — are  very  long  and  pointed,  and  are  admirably 
adapted  to  pierce  the  body  of  their  prey,  even  to  the 
vitals,  thus  killing  and  subsequently  tearing  the  ani- 
mal preparatory  to  feeding  upon  it.  The  herbivora  need 
no  such  aggressive  weapons,  and  in  them  the  molars  are 
so  constructed  as  to  grind  the  food,  their  teeth  resem- 
bling the  grindstones  of  the  miller.     The  teeth  of  man 


MOUTH  DIGESTION.  97 

have  characters  which  resemble  those  of  both  car- 
nivora  and  herbivora,  and  from  this  fact  it  may  be 
inferred  that  it  was  designed  that  man  should  have  a 
mixed  diet. 

The  function  of  the  teeth  in  man  is  to  thoroughly  sub- 
divide and  comminute  the  food  ;  and  this  function  is  an 
essential  part  of  the  process  of  digestion.  As  will  be 
seen  later,  during  digestion  certain  fluids  are  poured  into 
the  alimentary  canal  to  contribute  their  part  toward  the 
process.  These  fluids  cannot  act  properly  on  large,  com- 
pact masses  of  food.  While  their  action  is  not  entirely 
that  of  solution,  still,  in  order  to  fulfil  perfectly  their 
oflice  they  must  come  in  direct  contact  with  every  por- 
tion of  the  food.  This  contact  is  the  more  essential  be- 
cause the  given  time  in  which  to  act  is  not  unlimited,  and 
if  the  process  be  not  completed  within  the  allotted  time, 
digestion  will  be  performed  incompletely.  When  the 
chemist  desires  to  dissolve  a  substance  quickly  and  com- 
pletely, he  first  thoroughly  pulverizes  it  in  a  mortar. 
Likewise,  in  digestion  one  of  the  most  important  steps 
is  this  process  of  comminution  or  mastication.  If  masti- 
cation be  insufficiently  performed,  the  succeeding  steps 
in  the  process  of  digestion  are  seriously  interfered  with, 
and  indigestion  or  dyspepsia  results. 

Insufficient  mastication  is  one  of  the  commonest  causes 
of  indigestion,  and  many  dyspeptics  are  drugged  with 
remedies  prescribed  to  overcome  some  fancied  trouble  in 
the  stomach  when  they  should  be  sent  to  a  dentist.  De- 
fective mastication  may  be  due  to  various  causes.  The 
teeth  may  be  so  decayed  as  to  expose  sensitive  surfaces, 
and  when  food  which  is  at  all  hard  is  taken  into  the 
mouth,  the  discomfort,  or  sometimes  the  pain,  caused 
their  possessor  in  chewing  it  makes  the  performance  of 


98 


HUMAN  PHYSIOLOGY. 


the  act  incomplete,  and  the  food  is  swallowed  half  masti- 
cated ;  or  the  eater  may  be  in  too  great  a  hurry  and  not 
give  enough  time  to  this  important  act.  Whatever  the 
cause,  the  result  is  the  same ;  therefore  too  much  atten- 
tion cannot  be  given  to  this  process,  which  is  so  simple 
as  often  to  be  overlooked. 

Insalivation. — Coincident  with  mastication  is  the  act 
of  insalivation  or  the  incorporation  of  saliva  with  the 

food.  Saliva  is  the  secretion 
of  the  salivary  glands  (Fig.  6), 
which  comprise  the  parotid, 
submaxillary,  and  sublin- 
gual;  and  their  products,  to- 
gether with  that  of  the  mu- 
cous glands  of  the  mouth, 
form  the  saliva.  The  sali- 
vary glands  are  known  as 
"  compound  racemose ;"  they 
are  made  of  lobes,  and  these, 
again,  of  lobules  which  end 

Fig.  6. — Dissection  of  the  Side  of  the  Face, 
showing  the  salivary  glands  (after  Yeo) :    m  alvCOll.     ThcSC   glands  arC 
a,    sublingual    gland;    b,    submaxillary    ^f    ^^^    kinds  :    OUC   is    Called 
gland,   with    its    duct    opening    on    the 

floor  of  the  mouth  beneath  the  tongue  at  ''  mUCOUS,"  bcCaUSC  itS  CcUs 
d:  ..parotidgland  and  Us  duct,  which  ^^^^^^^  ^  ^^j^  of  which  UlU- 
opens  on  the  inner  side  oi  the  cheek. 

cin  is  a  constituent,  and  the 
other  is  called  "  serous,"  because  the  product  of  its  cells 
is  more  watery  in  its  nature,  or  is  called  "  albuminous," 
because  it  contains  serum-albumin.  The  sublingual  gland 
is  of  the  mucous  kind,  the  parotid  gland  is  of  the  albu- 
minous, while  the  submaxillary  gland  is  of  a  mixed  cha- 
racter, its  secretion  being  both  mucous  and  serous,  the 
alveoli  of  the  serous  kind  being  more  numerous.  The 
mucous  glands  of  the  mouth — "  buccal,"  as  they  are 


MOUTH  DIGESTION.  99 

called — secrete  mucus  only,  their  office  being  to  moisten 
the  mouth  when  mastication  is  not  going  on.  Mucus 
from  the  buccal  glands  mixes  also  with  the  products  of 
the  salivary  glands. 

Saliva  is  an  alkaline  fluid  with  a  specific  gravity 
of  1004,  and  is  secreted  to  the  amount  of  i^  litres 
daily.  It  is  occasionally  acid  a  few  hours  after  a  meal, 
and  may  be  slightly  acid  between  midnight  and  morn- 
ing. The  greatest  acidity  is  observed  two  or  three  hours 
after  breakfast  and  four  or  five  hours  after  dinner.  Saliva 
is  composed  of  99.5  per  cent,  of  water  and  0.05  per  cent, 
of  solids.  Of  the  solids,  one-half  is  inorganic,  the  salts 
being  principally  sodium  chloride,  calcium  carbonate, 
and  calcium  phosphate.  It  is  these  latter  two  salts  which 
accumulate  on  the  teeth,  forming  the  "  tartar."  They 
likewise  occasionally  form  "salivary  calculi"  in  the  in- 
terior of  the  salivary  glands  or  their  ducts,  and  require 
removal  by  the  surgeon.  Another  salt — which,  how- 
ever, is  not  invariably  present  in  the  saliva — is  potassium 
sulphocyanide,  which  has,  so  far  as  known,  no  physiolog- 
ical importance.  The  remaining  constituents  of  the  saliva 
are  mucin,  serum-albumin,  serum-globulin,  ptyalin,  and 
some  carbon  dioxide  in  solution.  Examined  under  the 
microscope,  there  are  seen  epithelial  scales  from  the 
mucous  membrane  of  the  mouth,  and  leucocytes,  prob- 
ably from  the  tonsils  and  elsewhere,  described  usually  as 
"  salivary  corpuscles."  Bacteria  and  portions  of  food  are 
commonly  found  in  saliva,  but  they  are  not  constituent 
parts,  but  rather  impurities. 

Office  of  Saliva. — The  office  of  saliva  is  twofold:  (i) 
chemical ;  and  (2)  mechanical. 

The  Clieinical  Action  of  Hn)nan  Sali^'a  is  due  to  the 
enzyme  ptyalin,  which  has  already  been  described.     This 


lOO  HUMAN  PHYSIOLOGY. 

enzyme  is  found  in  the  parotid  gland  of  new-born  children, 
but  not  in  the  submaxillary  gland,  and  it  is  not  found  as 
an  ingredient  of  the  saliva  of  animals  other  than  man.  It 
will  be  recalled  that  ptyalin  has  the  power  of  changing 
hydrated  starch  into  dextrin  and  maltose.  If  the  action 
of  the  ptyalin  be  long  continued,  some  of  the  maltose 
becomes  dextrose ;  but  as  the  time  required  to  accom- 
plish this  change  is  longer  than  the  ptyalin  continues  to 
act  during  ordinary  digestion,  this  change  probably  takes 
place  only  occasionally.  Ptyalin  has  no  action  on  raw 
starch.  It  will  be  seen,  therefore,  that  the  contribution 
which  the  chemical  action  of  saliva  makes  to  the  process 
of  digestion  is  not  very  great,  and  yet  it  is  not  wholly  to 
be  ignored. 

Mechanical  Office  of  Saliva. — The  principal  office  of 
saliva  is  undoubtedly  mechanical.  While  the  teeth  are 
thoroughly  comminuting  the  food,  they  are  at  the  same 
time  working  saliva  into  the  interstices  which  they  make 
between  the  particles  of  the  food.  This  process  not  only 
facilitates  the  chemical  action  of  the  ptyalin,  but  it  tends 
also  to  keep  the  particles  separated,  so  that  when  the 
food  reaches  the  stomach  the  gastric  juice  may  the  more 
readily  permeate  it  and  produce  its  characteristic  action. 
Saliva  aids  also  in  softening  the  food,  thus  enabling  the 
process  of  deglutition,  or  swallowing,  more  easily  to  be 
performed.  The  secretion  of  the  mucous  glands  of  the 
mouth  is  of  special  importance  in  this  act,  the  consistency 
of  the  mucus  secreted  being  "ropy"  and  possessing  great 
lubricating  properties.  Saliva  is  intimately  connected 
with  the  sense  of  taste.  Only  soluble  substances  are 
sapid ;  that  is,  excite  the  sense  of  taste.  Insoluble  sub- 
stances have  no  taste.  It  is  for  this  reason,  among  others, 
that  calomel  is  such  an  excellent  cathartic  for  children ; 


MOUTH  DIGESTION. 


lOI 


being  insoluble,  it  is  tasteless,  and  they  readily  swallow 
it.  Soluble  substances  not  already  in  a  state  of  solution 
are  dissolved  by  the  saliva,  and  in  this  condition  excite 
the  sense  of  taste.  When  in  a  febrile  or  other  state,  in 
which  the  secretion  of  saliva  is  greatly  diminished,  de- 
glutition is  difficult  and  the  sense  of  taste  is  markedly 
deteriorated. 

A  portion  of  the  food  having  been  thoroughly  mas- 
ticated and  insalivated,  it  is  collected  by  the  tongue 
and  cheeks  into  a  small  mass  known  as  the  "  aUment- 
ary  bolus,"  which  now  undergoes  the  process  of  de- 
glutition. 

Deglutitio?i,  or  the  act  of  swallowing,  consists  in  the 
passage  of  the  food  from  the  mouth, 
through  the  pharynx  and  oesopha- 
gus (Fig.  7)  to  the  stomach.  Deg- 
lutition is  divided  into  three  stages 
or  steps.  In  the  first  stage  the  ali- 
mentary bolus  is  carried  by  the 
tongue  back  into  the  pharynx;  as 
the  bolus  passes  over  the  soft  palate 
it  receives  a  coating  of  the  very 
viscid  secretion  of  the  mucous 
glands,  which  are  here  situated. 
This  first  step  is  purely  voluntaiy, 
entirely  under  the  control  of  the   Fig.  7.— Muscular  coat  of  the 

HI  I  r  1  i_  Pharynx  and  (Esophagus 

,  and  may  be  performed  or  not 

as  desired.  After  the  bolus,  however,  reaches  the  phar- 
ynx, it  passes  from  the  control  of  the  will.  If  one  were 
informed  at  this  stage  of  the  act  that  the  bolus  contained 
the  most  virulent  poison,  it  could  not  be  rejected,  but  he 
would  be  compelled  to  swallow  it.  In  this,  the  second 
stage,  the  bolus  passes  through  the  pharynx,  under  the 


102  HUMAN  PHYSIOLOGY. 

influence  of  the  constrictor  muscles,  into  the  oesophagus. 
The  tongue  is  drawn  backward,  the  isthmus  of  the  fauces 
is  contracted,  and  the  soft  palate,  the  larynx,  and  the 
pharynx  are  elevated,  so  that  the  entrance  of  food 
into  either  the  posterior  nares  or  the  larynx  is  pre- 
vented ;  the  constrictor  muscles  then  contracting,  the 
food  is  carried  through  the  pharynx  into  the  oesoph- 
agus. 

It  was  formerly  thought  that  the  function  of  the  epi- 
glottis was  to  prevent  the  entrance  of  food  into  the  lar- 
ynx, and  its  relations  would  seem  to  justify  such  a  view, 
but  observation  shows  that  this  view  is  not  true.  In  the 
first  place,  this  organ  is  present  only  in  mammals,  and  is 
absent  in  other  vertebrates,  although  the  process  of  deg- 
lutition is  performed  as  well  in  the  former  as  in  the  latter. 
Then,  too,  a  dog  whose  epiglottis  has  been  excised  ex- 
periences no  difficulty  in  swallowing  either  solids  or 
liquids.  The  elevation  of  the  larynx  and  the  backward 
drawing  of  the  tongue  are  alone  sufficient  to  protect  the 
glottis  from  the  entrance  of  food. 

From  the  pharynx  the  food  passes  into  the  oesophagus, 
and  through  the  latter  into  the  stomach ;  this  constitutes 
the  third  stage,  which  is  also  involuntary  in  its  character, 
and  which  is  brought  about  by  the  successive  contrac- 
tions of  the  muscular  coat  of  the  oesophagus.  In  the 
act  of  rumination,  which  is  characteristic  of  the  rumi- 
nants, and  in  vomiting,  there  is  a  reversal  of  this  action, 
so  that  the  contents  of  the  stomach  are  carried  to  the 
pharynx. 

In  deglutition  the  food  does  not  pass  through  the 
oesophagus  by  virtue  of  the  force  of  gravity.  This  is 
shown  by  the  fact  that  deglutition  may  be  performed  as 
successfully  when  an  individual  is  standing  on  his  head 


STOMACH  DIGESTION.  IO3 

as  when  he  is  on  his  feet,  and  many  animals,  such  as  the 
horse  and  dog,  always  perform  the  act  in  opposition  to 
gravity.  This  act  is  brought  about  by  a  series  of  mus- 
cular contractions  which  begin  in  the  mouth  and  end  at 
the  stomach.  During  deglutition  the  ptyalin  continues 
its  action  on  the  starch ;  other  than  this  action  no  chem- 
ical change  takes  place  in  the  food  while  it  is  passing 
through  the  oesophagus.  The  mucous  membrane  of 
this  canal  furnishes  a  mucus  which  has  no  digestive 
action,  but  is  simply  a  lubricant. 


B.  Stomach  Digestion. 

The  food,  having  reached  the  stomach,  now  undergoes 
stomach  or  gastric  digestion.  The  stomach  in  the  human 
adult  is  about  35  centimetres  in  length  and  12  in  width, 
and  when  distended  it  may  contain  3  litres. 

Coats  of  tJic  Stomach. — The  stomach  is  composed  of 
four  coats:  serous,  muscular,  submucous,  and  mucous. 
The  serous  coat  is  a  reflection  of  the  peritoneum.  The  sub- 
mucous coat,  which  contains  the  nerves  and  blood-vessels, 
is  of  special  interest  as  giving  to  the  mucous  coat  great 
mobility  and  as  permitting  it  to  form  folds,  called  "  rugae," 
when  the  cavity  is  empty.  This  structure  is  in  striking 
contrast  with  the  anatomical  structure  of  the  uterus,  in 
which  organ,  the  submucous  coat  being  absent  and  the 
mucous  lying  directly  upon  the  muscular  coat,  there  is  a 
total  want  of  mobility  in  the  membrane.  Aside  from 
this  statement  neither  the  serous  nor  the  submucous  coat 
has  any  special  physiological  interest.  The  muscular 
coat  is  composed  of  three  layers  :  longitudinal,  circular, 
and  oblique.  The  lous^itudiiial  layer  is  made  up  of  fibres 
continuous  with  similar  fibres  of  the  oesophagus,  and  is 


104  HUMAN  PHYSIOLOGY. 

most  external — that  is,  immediately  beneath  the  peri- 
toneum. These  fibres  radiate  from  the  oesophageal  or 
cardiac  orifice,  and  are  especially  abundant  in  the  region 
of  the  greater  and  lesser  curvatures.  They  extend  to 
the  intestine,  where  they  form  a  layer  of  the  muscular 
coat  of  that  organ.  The  circular  layer  is  situated  inter- 
nal to  the  longitudinal,  and,  as  the  name  implies,  its 
fibres  encircle  the  stomach — that  is,  are  in  general  at 
right  angles  to  the  longitudinal  axis  of  the  stomach. 
At  the  pyloric  orifice  of  the  stomach,  where  the  duo- 
denum begins,  these  circular  fibres  are  aggregated  in 
such  number  as  to  receive  the  name  of  "  pyloric  muscle." 
Their  projection  into  the  interior  of  the  organ  at  this 
location  with  its  covering  of  mucous  membrane  con- 
•  stitutes  the  pyloric  valve.  The  oblique  layer  is  found 
especially  at  the  cardiac  extremity  of  the  stomach. 

The  mucous  coat,  or  mucous  membrane,  is  soft  and 
velvety.  Near  the  cardiac  orifice  the  membrane  is  about 
i^  millimetres  in  thickness,  and  near  the  pylorus  2  milli- 
metres, while  in  general  between  these  two  points  its 
thickness  is  about  i  millimetre.  Its  surface  is  composed 
of  columnar  epithelium,  which  secretes  the  mucus  found 
in  the  stomach  in  the  intervals  of  digestion,  this  mucus 
being  a  constituent  of  the  gastric  juice. 

In  the  mucous  membrane,  and  forming  a  part  of  it, 
are  two  sets  of  glands,  the  "  pyloric  "  glands,  so  called 
from  their  abundance  in  the  pyloric  portion  of  the 
stomach,  and  the  "cardiac"  glands  (Fig.  8),  which  are  so 
called  because  of  their  occurrence  in  the  cardiac  region. 
The  ducts  of  both  sets  are  lined  by  columnar  epithelium 
continuous  with  that  covering  the  mucous  membrane. 
In  the  tubes  of  the  pyloric  glands  are  granular  cells 
called  "  chief  cells."     The  same  kind  of  cells  is  found  in 


STOMACH  DIGESTION. 


105 


the  tubes  of  the  cardiac  glands,  and  beneath  these  cells 
— that  is,  between  them  and  the  basement  membrane — are, 
besides,  larger  cells,  which  are  ovoid  in  shape  and  which 


Fig.  8. — Cardiac  Glands. 
Diagram  showing  the  Relation  of  the  Ultimate  Twigs  of  the  Blood-vessels,  K  and 
A,  and  of  the  absorbent  radicals,  L,  to  the  glands  of  the  stomach,  and  the  different 
kinds  of  epithelium — namely,  above,  cylindrical  cells  ;  small  pale  cells  in  the  lumen, 
outside  which  are  the  dark  ovoid  cells. 

are  known  as  "  parietal  cells."  These  cells  cause  the  base- 
ment membrane  against  which  they  lie  to  bulge  out. 
The  chief  cells  are  regarded  as  producing  the  pepsin- 
ogen which  is  converted  into  the  pepsin  of  the  gastric 
juice,  and  the  parietal  cells  as  producing  the  hydro- 
chloric acid.  The  vascularity  of  the  stomach  is  very 
great.  In  the  intervals  of  digestion  the  mucous  mem- 
brane is  of  a  pale  pinkish  color,  while  during  active  di- 
gestion its  color  is  a  bright  red.  This  change  in  color  is 
due  to  the  greatly  increased  amount  of  blood  present  in 
the  blood-vessels  of  the  or^an  at  this  time. 


I06  HUMAN  PHYSIOLOGY. 

Prior  to  1822  the  process  of  stomach  digestion  was 
little  understood.     During  that  year  Alexis  St.  Martin,  a 

Canadian  boatman,  was  so 
injured  by  the  accidental 
discharge  of  a  gun  that 
when  the  wound  healed 
there  remained  in  his 
side  a  permanent  opening 
(nearly  2)^  centimetres  in 
diameter),  which  com- 
municated with  the  cavity 
of  the  stomach  (Fig.  9). 
Fig  q— left  Dreist  and  Sidt  ^<.lcct  posi-  Dr.Beaumont, thc surgcon 

tion)    showing  perforation  of  the  walls  of     .       ^  ^^  ^^^  ^^^ 

the  stomach  of  Alexis  St.  Martin.  o  ' 

subsequently  others,  car- 
ried on  a  series  of  experiments  and  observations  extend- 
ing through  years,  and  the  present  knowledge  of  stomach 
digestion  is  largely  based  upon  this  remarkable  case. 

During  the  intervals  of  digestion  the  mucous  mem- 
brane of  the  stomach  is  pale  in  color,  and  is  covered  with 
a  transparent  and  viscid  mucus  which  is  neutral  or  alka- 
line in  reaction.  This  mucus  is  the  product  of  the  epi- 
thelium of  the  mucous  membrane.  After  food  has  en- 
tered the  stomach  drops  of  gastric  juice  appear  at  the 
mouths  of  the  glands. 

Quantity  of  Gastric  Juice. — The  amount  of  gastric  juice 
daily  secreted  is  difficult  of  determination,  and  it  is  not 
surprising  that  authorities  should  differ  so  much  on  this 
point.  Dr.  Beaumont  estimated  it  to  be  180  grammes 
in  the  case  of  St.  Martin,  while  others  place  it  as  high 
as  7  litres,  or  one-tenth  of  the  weight  of  the  body.  The 
gastric  juice  is  never  in  large  quantity  in  the  stomach  at 
any  one  time.     It  is  secreted  gradually  by  the  glands,  is 


STOMACH  DIGESTION.  10/ 

poured  out  into  the  cavity  of  the  stomach,  where  it  per- 
meates the  food,  is  passed  on  into  the  small  intestine, 
where  it  is  absorbed  by  the  blood-vessels,  and  is  then 
returned  to  the  circulation,  from  which  its  constituents 
were  derived.  It  has  the  following  properties  :  it  is  clear, 
slightly  yellowish  in  color,  and  strongly  acid.  Its  specific 
gravity  is  from  looi  to  loio. 

Composition  of  Hiiniaii  Gastric  Juice  mixed  zvith  Saliva. 
— As  can  readily  be  understood,  it  is  impossible  to  obtain 
gastric  juice  unmixed  with  particles  of  food  or  saliva  or 
other  foreign  substances,  hence  an  accurate  analysis  can- 
not be  given.  The  analysis  of  Schmidt  of  gastric  juice 
from  a  women  having  a  gastric  fistula  is  as  follows  : 

Percentages. 

Water 99.4400 

Organic  substances  (pepsin,  peptones, 

and  rennin) -3195 

Free  hydrochloric  acid .0200 

Calcium  chloride 0061 

Sodium         "         .    .    • .1464 

Potassium     "         -OS  50 

Calcium         | 

Magnesium  V  phosphates 0125 

Ferrum         J 

Loss 0005 

100.0000 

The  constituents  of  the  gastric  juice  of  any  special 
physiological  interest  arc  hydrochloric  acid,  pepsin,  and 
rennin.  It  was  at  one  time  a  matter  of  dispute  whether 
the  acidity  of  this  fluid  was  due  to  hydrochloric  or  to 
lactic  acid,  but  there  is  now  a  unanimity  of  opinion  that 
it  is  the  former.     If  lactic  acid  be  present,  it  is  probably 


Io8  HUMAN  PHYSIOLOGY. 

due  to  lactic  fermentation  which  has  taken  place  in  the 
carbohydrates  of  the  food  when  these  are  in  excess. 
This  fermentation  may  go  on  to  the  formation  of  acetic 
and  butyric  acids,  these  changes  being  doubtless  due  to 
the  presence  of  micro-organisms. 

Hydrochloric  Acid. — The  amount  of  free  hydrochloric 
acid  in  human  gastric  juice  varies  from  0.05  to  0.3  per 
cent.  Several  of  the  best  authorities  give  the  average  as 
between  0.2  and  0.3  per  cent. 

Pepsin. — The  "  chief"  cells  of  both  the  cardiac  and  the 
pyloric  glands,  during  the  intervals  of  digestion,  produce 
the  zymogen  pepsinogen,  which  has  no  digestive  action 
upon  proteids.  The  parietal  cells  produce  hydrochloric 
acid,  the  action  of  which  upon  the  pepsinogen  converts 
the  latter  into  pepsin.  This  acid  is  formed  from  the 
chlorides  which  are  brought  to  the  glands  by  the  blood. 
The  action  of  pepsin  upon  proteids  in  presence  of  hy- 
drochloric acid  has  already  been  studied.  To  recapit- 
ulate :  The  proteid  is  first  converted  into  acid-albumin, 
or  syntonin  (some  authorities,  it  will  be  remembered, 
limit  the  term  "syntonin"  to  that  particular  acid-albumin 
which  is  produced  from  myosin),  which  passes  into  al- 
bumose,  and  this  into  peptone  or  peptone  with  some 
albumose. 

Renniji. — There  is  in  human  gastric  juice  another  en- 
zyme, rennin,  which  is  produced  from  renninogen,  a 
zymogen  which,  like  pepsinogen,  is  the  product  of  the 
"  chief"  cells  of  the  gastric  glands.  It  is  interesting  to  note 
in  this  connection  that  some  observers  have  found  that 
this  enzyme  was  absent  from  the  gastric  juice  in  carcinoma 
of  the  stomach,  atrophy  of  its  mucous  membrane,  and  in 
some  cases  of  gastric  catarrh.  It  will  be  remembered  that 
rennin  coagulates  the  casein  of  milk.      In  the   gastric 


STOMACH  DIGESTION.  IO9 

digestion  of  this  important  food  the  coagulation  of  the 
casein  is  a  prehminary  step.  Mothers  are  sometimes 
frightened  when  their  children,  seemingly  in  perfect 
health,  vomit  curdled  milk,  but  this  curdling  of  milk 
is  a  normal  process,  and  the  only  abnormality  consists 
in  its  regurgitation,  which  is  usually  due  to  over-feeding. 

As  matter  of  secondary  interest  there  is  some  evidence 
that  in  gastric  juice  there  is  a  lactic-acid  ferment  which 
changes  the  lactose  of  milk  into  lactic  acid ;  another 
ferment  which  converts  cane-sugar  into  glucose;  and 
still  another,  a  fat-splitting  one,  which  breaks  up  fats 
into  glycerin  and  fatty  acids,  but  the  amount  of  these 
materials  changed  in  the  stomach  is  not  very  great. 
Gastric  juice  does  not  change  starch. 

The  albuminoids  are,  some  of  them,  as  has  been  seen, 
converted  into  peptones,  but  they  have  little  nutritive 
value.  The  one  which  is  more  than  any  other  looked 
upon  as  contributing  to  nutrition  is  gelatin.  But  gelatin 
is  not  available  directly  for  the  growth  and  repair  of  tis- 
sues. It  has  an  "  albumin-sparing  "  action.  Much  less 
flesh  is  required  by  an  animal  if  fat  be  taken  with  the 
flesh,  this  being  spoken  of  as  the  "  albumin-sparing " 
action  of  fat.  The  same  is  true  of  gelatin.  Gelatin 
forms  urea,  and  when  present  in  the  food  in  large  amount 
the  kidneys  are  excited  to  increased  action. 

Chyme. — The  mixture  of  food  and  gastric  juice  is 
called  "  chyme."  Chyme  is  not  a  mixture  having  a  con- 
stant composition :  it  varies  according  to  the  articles  of 
food  ingested. 

There  are,  in  addition  to  the  presence  of  pepsin  and 
hydrochloric  acid,  two  other  requisites  for  normal  diges- 
tion. The  temperature  must  be  favorable,  and  this  is  found 
in  the  stomach  where  the  thermometer  indicates  38°  C ; 


I  lO  HUMAN  PHYSIOL  OGY. 

the  other  requisite  is  the  muscular  movements  of  the 
stomach. 

Muscular  Movements  of  Stomach. — In  the  empty  con- 
dition of  the  stomach  the  direction  of  the  greater  curva- 
ture is  downward  and  that  of  the  lesser  curvature  up- 
ward ;  but  as  food  enters  and  begins  to  fill  this  organ,  it 
rises  upward  in  such  a  manner  that  when  filled  the  greater 
curvature  is  forward  and  the  lesser  curvature  backward. 
From  the  time  that  food  enters  the  cavity  of  the  stomach 
until  it  has  all  passed  out  the  muscular  coat  of  the  stom- 
ach is  in  action.  The  walls  are  in  contact  except  where 
separated  by  food,  and  are  constantly  rubbing  against  each 
other,  or  against  that  which  separates  them,  with  a  rotatory 
motion.  The  masses  of  food  are  by  this  means  broken  up 
and  the  gastric  juice  is  incorporated  with  them.  In  the 
stomach  of  the  cow  it  is  not  unusual  to  find  balls  of 
considerable  size,  made  up  of  hair  which  the  animal  has 
licked  from  her  hide  and  swallowed.  These  balls  are 
perfectly  spherical,  and  are  undoubtedly  formed  by  this 
rotatory  or  churning  motion  of  the  muscular  coats  of  the 
stomach.  There  is,  besides  this,  a  movement  which  car- 
ries the  food  toward  the  pyloric  orifice,  and  which  is 
known  as  "  vermicular"  or  "peristaltic."  If  any  portion 
of  the  food  as  it  reaches  this  part  of  the  stomach  be 
sufficiently  liquid,  the  pyloric  muscle  relaxes  and  per- 
mits it  to  pass  through  into  the  duodenum ;  otherwise  it 
is  carried  back,  and  is  again  brought  under  the  influence 
of  the  rotatory  movements  of  the  stomach.  While 
during  the  greater  part  of  stomach  digestion  the  pyloric 
muscle  keeps  the  pylorus  closed,  only  relaxing  to  permit 
the  prepared  material  to  pass,  at  the  close  of  the  act  it 
remains  so  relaxed  that  solid  particles  can  pass  into  the 
duodenum  without  difficulty. 


STOMACH  DIGESTION.  1 1 1 

Self -digestion  of  Stomach. — One  of  the  interesting  and 
still  unexplained  physiological  enigmas  is :  Why  does 
not  the  stomach,  which  is  proteid  in  its  nature,  undergo 
self-digestion  during  life  ?  It  is  known  that  when  death 
takes  place  during  the  period  of  active  stomach  diges- 
tion erosion  of  the  mucous  membrane,  and  even  perfora- 
tion of  the  wall  of  the  stomach,  may  occur.  As  this 
takes  place  at  the  most  dependent  portion,  where  the  gas- 
tric juice  naturally  gravitates,  the  explanation  is  simple. 
But  if  this  self-digestion  can  occur  after  death,  why^  not 
during  life  ?  No  satisfactory  answer  to  this  question  has 
yet  been  given,  although  many  theories  have  been  ad- 
vanced. 

Results  of  Stomach  Digestion. — The  following,  then,  are 
the  results  of  stomach  digestion  :  The  proteids  are  con- 
verted into  peptones ;  in  the  case  of  milk  the  proteid 
casein  is  first  coagulated,  and  then  changed  into  peptone. 
Starch  is  not  changed  by  the  gastric  juice,  though  the 
action  of  the  ptyalin,  which  commenced  in  the  mouth  and 
was  continued  in  the  oesophagus,  does  not  cease  in  the 
stomach  until  the  food  becomes  so  acid  as  to  prevent  the 
further  action  of  the  enzyme.  Some  of  the  carbohydrates 
may,  as  has  been  seen,  undergo  the  lactic  fermentation. 

If  fat  be  present  in  the  food  in  the  free  state,  as  in  oil, 
it  is  made  more  fluid  by  the  heat  of  the  stomach  ;  if  it 
be  in  the  form  of  adipose  tissue,  in  which  the  fat  is  en- 
closed in  sacs,  forming  the  adipose  vesicles,  these  sacs, 
being  proteid  in  their  nature,  are  acted  upon  by  the  gas- 
tric juice  as  are  other  proteids,  and  the  fat  is  set  free, 
when  it  is  acted  upon  in  the  same  manner  as  the  free  fat 
just  referred  to.  Some  of  the  fat  may  be  split  up  into 
glycerin  and  fatty  acids,  but  the  greater  part  passes  on 
into  the  duodenum. 


1 1 2  HUMAN  PHYSIOL  OGY. 

The  stomach  contains  gases  which  in  the  dog  have 
been  found  to  be  nitrogen,  oxygen,  and  carbon  dioxide. 
The  hydrochloric  acid  that  is  normally  present  in  gas- 
tric juice  prevents  the  formation  of  gases  from  fermen- 
tative changes  in  the  food.  The  stomach-gases  are  at- 
tributable to  the  air  incorporated  with  the  food  in  the 
mouth,  and  to  the  saliva,  in  which,  as  we  have  seen, 
carbon  dioxide  exists  in  solution.  It  is  also  probable 
that  there  is  some  escape  of  gases  from  the  intestine  into 
the  stomach. 

Duration  of  Stomach  Digestion. — The  duration  of  stom- 
ach digestion  is  variable,  and  depends  upon  several  cir- 
cumstances, among  which  is  the  composition  of  the 
stomach-contents.  Some  kinds  of  food  remain  in  the 
stomach  longer  than  others.  Stomach  digestion  may 
in  general  be  said  to  be  from  one  and  a  half  to  five 
and  a  half  hours,  according  to  the  nature  of  the  food. 
The  following  table  contains  a  list  of  some  of  the  sub- 
stances with  which  Dr.  Beaumont  experimented,  and  the 
length  of  time  they  remained  in  the  stomach : 

Kind  of  Food.  Time. 

Pig's  feet  and  tripe i  hour. 

Salmon i 

Milk 2  hours. 

Potatoes,  roasted 2 

Roast  turkey 2>^    " 

Soft-boiled  eggs 2>^   " 

Beefsteak,  broiled 2%   "  . 

Hard-boiled  eggs 3 

Potatoes,  boiled SH   " 

Pork,  boiled 4)4 

"      roast .    .    .  5/i   " 


STOMACH  DIGESTION.  1 1 3 

The  above  table,  and  others  of  hke  nature,  are  to  be 
very  cautiously  made  use  of  in  determining  the  digest- 
ibihty  of  the  different  foods.  The  observations  here  re- 
corded simply  indicate  the  length  of  time  the  respective 
articles  remained  in  the  stomach,  and  nothing  more.  Sub- 
stances are  digested  vj\\Qn  they  are  in  condition  to  be  ab- 
sorbed, and  not  until  then.  Whenever  any  portion  of 
the  food  is  rendered  sufficiently  liquid,  it  is  liable  to  pass 
out  from  the  stomach,  although  there  are  other  factors 
than  this  liquid  character  of  the  food.  If  two  different 
articles  of  food  were  in  the  stomach  at  the  same  time, 
one  might  pass  out  from  that  organ  into  the  small  in- 
testine in  one  hour,  while  the  other  might  remain  in  the 
stomach  two  hours.  From  this  fact  alone  one  would 
not  be  justified  in  assuming  that  the  one  substance  v/as 
twice  as  digestible  as  the  other,  for  the  former  might  not 
at  the  time  it  left  the  stomach  have  been  prepared  for 
absorption,  but  might  require  several  hours  for  such 
a  change  after  it  reached  the  small  intestine ;  while  the 
latter,  although  it  remained  in  the  stomach  an  hour  after 
the  former  had  left  it,  might  at  the  time  it  left  the  stom- 
ach have  been  in  a  condition  to  pass  at  once  into  the 
blood. 

The  practical  use  of  tables  showing  the  length  of  time 
that  different  substances  remain  in  the  stomach  seems 
to  be  to  determine  of  what  the  food  should  consist 
when  this  organ  is  unable  to  perform  its  function  in  a 
normal  manner  and  it  is  considered  wise  to  lighten  its 
labors  as  much  as  possible.  For  this  purpose  such  food 
should  be  selected  as  will  remain  in  the  stomach  but  a 
short  time,  even  though  it  pass  out  in  an  undigested 
state,  for,  as  will  hereafter  be  seen,  the  peptonizing  func- 
tion is  as  well  carried  on  in  the  small  intestine  as  in  the 
8 


I  1 4  HUMAN  PH  YSIOL  OGY. 

stomach,  and  in  a  disabled  condition  of  the  latter  organ 
the  former  will  supplement  it.  In  the  dog  so  thoroughly 
may  digestion  be  performed  by  the  intestines  alone,  with- 
out the  aid  of  the  stomach,  that  this  latter  organ  has 
been  almost  completely  removed,  yet  the  animal  has 
been  kept  alive  in  excellent  health  and  strength.  The 
proper  foods  under  these  circumstances  are  those  that 
are  liquid  when  ingested  or  are  readily  liquefied  in  the 
stomach. 

As  above  stated,  the  length  of  time  that  food  remains 
in  the  stomach  is  not  determined  by  its  consistency 
alone.  One  of  the  important  factors  is  the  amount  of 
hydrochloric  acid  present;  thus  when  this  acid  is  rel- 
atively great  it  seems  to  act  as  an  irritant,  and  the  pyloric 
muscle  relaxes  more  readily  than  when  the  amount  is 
less. 

Some  light  has  been  thrown  on  this  question  of  the 
duration  of  stomach  digestion  by  the  application  of 
methods  of  obtaining  and  examining  the  contents  of 
the  stomach  for  diagnostic  purposes.  To  ascertain  how 
far  the  digestive  process  is  interfered  with,  "  trial "  meals 
are  given.  The  stomach  is  evacuated  by  means  of  a 
soft-rubber  stomach-pipe  after  a  proper  time,  and  in- 
spection shows  how  far  the  process  of  digestion  has 
advanced.  Ewald's  "  trial  "  meal  consists  of  one  water- 
roll  weighing  35  grammes  and  a  cup  of  tea  or  300  or 
400  cc.  of  water.  After  this  food  has  been  two  and  a 
half  hours  in  the  stomach  that  organ  will  be  found  empty; 
in  one  case  the  food  had  disappeared  after  one  hour. 
Riegel's  "  trial  "  meal  consists  of  a  cup  of  broth,  400 
grammes ;  beef,  60  grammes ;  and  bread,  50  grammes. 
After  seven  hours  the  stomach  will  be  found  empty. 

Artificial  Gastric  Juice. — In  addition  to  the  observa- 


STOMACH  DIGESTION.  1 1  5 

tions  of  Beaumont  and  others  upon  cases  of  gastric 
fistula,  many  experiments  have  been  made  with  an  arti- 
ficial gastric  juice  made  by  extracting  the  pepsin  from 
the  mucous  membrane  of  the  stomach  of  the  pig  with 
glycerin,  and  adding  to  this  glycerin-extract  0.2  per  cent, 
of  hydrochloric  acid.  The  results  of  these  experiments 
are,  however,  not  to  be  regarded  as  identical  with  those 
that  take  place  in  the  stomach  of  a  living  human  being. 
The  factors  in  the  problem  are  many,  and  some  of  them 
are  still  undetermined,  as,  for  instance,  the  action  of  the 
gastric  juice  on  the  different  proteids. 

Effects  of  Alcohol  on  Digestion. — Much  has  been  written 
on  the  effects  of  alcoholic  and  other  beverages  upon  di- 
gestion, and  the  testimony  is  very  conflicting.  Thus  one 
authority  states  that  the  action  of  pepsin  is  retarded  tem- 
porarily by  the  presence  of  alcohol,  but  after  the  latter  is 
absorbed,  which  occurs  very  rapidly,  there  is  an  increased 
flow  of  very  active  gastric  juice;  another  says  that  alco- 
hol retards,  and  even  prevents,  digestion ;  while  a  third 
maintains  that  it  aids  digestion  from  the  beginning  of  its 
entrance  into  the  stomach.  The  fact  probably  is  that  in 
each  of  these  opinions  there  is  some  truth,  and  that  the 
effects  of  alcohol  vary  according  to  the  conditions  present. 
The  first  principle  which  may  be  laid  down  is  that  alco- 
hol, under  ordinary  circumstances,  is  not  needed  to  aid 
digestion,  but  it  is  to  be  regarded  as  an  agent  which, 
under  the  direction  of  the  physician,  may  be  employed 
to  assist  him  in  the  treatment  of  diseased  conditions. 
About  95  per  cent,  of  the  alcohol  taken  into  the  body 
is  oxidized,  carbon-dioxide  and  water  resulting.  To  this 
extent  it  serves  to  produce  heat,  and  whenever,  therefore, 
the  supply  of  food  is  insufficient,  alcohol  is  of  value  in 
preventing  so  far  as  possible  the  using  up  of  the  tissues 


1 1 6  HUMAN  PHYSIO  LOG  Y. 

of  the  body.  The  above  statement  is  true  if  an  amount 
not  exceeding  two  ounces  be  taken  daily,  but  when  an 
abundance  of  food  can  be  obtained  the  use  of  alcohol 
offers  no  advantages.  Alcohol  in  small  doses  excites 
the  nervous  system,  and  if  this  stimulation  be  kept  up 
harm  must  result,  for  after  the  stimulation  there  is  a  de- 
pressing reaction.  The  action  of  alcohol  on  the  vascular 
system  is  to  excite  the  latter  and  to  increase  the  circula- 
tion of  the  blood ;  thus  in  a  given  time  both  nerves  and 
muscles  are  supplied  with  more  blood.  It  is  this  action 
which  produces  the  sense  of  warmth  when  alcohol  has 
been  taken,  but  this  warmth  is  purely  subjective,  the 
thermometer  showing  that  alcohol,  even  in  moderate 
amount,  actually  lowers  the  temperature.  The  blood- 
vessels of  the  skin  dilate  under  the  influence  of  alcohol, 
and  there  is  a  loss  of  heat  by  radiation  from  the  blood. 
The  pulse  is  smaller  and  is  increased  in  rate,  while  its 
strength  is  diminished,  showing  action  upon  the  heart. 
One  who  has  made  a  special  study  of  the  action  of  alco- 
hol upon  the  nervous  system  says  that  it  seems  to  in- 
duce progressive  paralysis,  the  judgment  being  affected 
first,  although  the  imagination  and  emotions  may  be 
more  than  usually  active ;  the  motor  centres  and  speech 
are  next  affected,  then  the  cerebellum,  then  the  spinal 
cord ;  and  finally,  if  the  quantity  taken  be  large,  death 
may  result. 

An  instructive  lesson  may  be  obtained  by  observing 
the  effect  of  alcohol  upon  animal  tissues  immersed  in  it. 
It  is  known  that  such  tissues  are  dried  up  and  shrivelled  ; 
in  the  same  way,  although  to  a  very  much  less  degree, 
the  proteids  of  the  cells  of  the  mucous  membrane  are 
affected  in  the  form  of  coagulation  when  alcohol  is  taken 
into  the  empty  stomach  in  concentration,  as  in  whiskey 


S  TO  MA  CH  DICES  TION.  1 1 7 

or  in  brandy.  When  diluted  the  action  of  alcohol  is  less 
pronounced.  When  the  stomach  contains  food  the  lia- 
bility of  injury  is  less,  as  then  the  alcohol  is  diluted  by 
the  liquids,  and,  if  there  be  proteids  in  the  food,  some  of 
these  are  coagulated,  the  mucous  membrane  thus  being 
doubly  protected.  The  frequent  imbibing  of  spirituous 
liquors  on  an  empty  stomach,  as  practised  by  so  many, 
is  the  most  injurious  form  of  alcohol-taking.  Not  only 
are  the  nervous  and  vascular  systems  affected,  but  a 
catarrhal  condition  of  the  digestive  organs  is  also  pro- 
duced. If  the  alcohol  contain  impurities,  such  as  fusel 
oil,  its  action  is  still  more  harmful. 

Before  leaving  the  process  of  stomach  digestion  it  may 
be  well  to  call  attention  to  the  fact  that  the  hydrochloric 
acid  of  the  gastric  juice  has  a  germicide  action  on  some 
of  the  pathogenic  bacteria.  This  action,  on  the  one  hand, 
is  not  true  of  all  pathogenic  bacteria,  for  those  which 
produce  tuberculosis  and  anthrax  are  not  destroyed  by 
gastric  juice ;  on  the  other  hand,  the  cholera  spirillum, 
the  germ  of  Asiatic  cholera,  is  destroyed  in  normal  gas- 
tric juice.  Experiments  have  demonstrated  this  fact,  and 
also  that  if  a  solution  of  soda  be  injected  into  the  stom- 
ach, the  vitality  of  this  micro-organism  is  not  destroyed. 
It  is  therefore  of  the  utmost  importance,  during  the 
prevalence  of  cholera,  to  keep  the  digestive  organs  in 
normal  condition.  Anything  which  tends  to  produce  a 
catarrhal  condition  of  the  stomach,  as  alcohol  in  excess, 
will  be  likely  to  increase  the  alkaline  mucus,  and  thus 
make  the  conditions  favorable  should  the  spirilla  find 
their  way  into  the  stomach  in  solid  or  in  liquid  food.  It 
is  probably  by  interfering  with  normal  digestion,  inhibit- 
ing the  production  of  hydrochloric  acid,  that  fear  con- 
duces toward  the  spread  of  this  disease.     Dr.  Beaumont 


Il8  HUMAN  PHYSIOLOGY. 

in  the  case  of  St.  Martin  observed  that  when  his  temper 
was  irritated  the  secretion  of  gastric  juice  was  greatly 
interfered  with  or  even  suspended.  Unusual  fatigue  and 
a  condition  of  fever  would  produce  the  same  results.  It 
is  a  matter  of  common  experience  that  fear,  worry,  anger, 
the  receipt  of  unexpected  news,  either  joyous  or  sorrow- 
ful, will  oftentimes  seriously  interrupt  gastric  digestion. 
Therefore  at  all  times  the  endeavor  should  be  to  keep 
the  mind,  during  the  period  of  digestion  at  least,  free 
from  these  disturbing  agencies. 

The  acidity  of  gastric  juice,  even  in  comparative  health, 
is  not  always  the  same :  it  may  be  in  excess  or  it  may  be 
deficient.  In  the  latter  condition,  the  antifermentative 
action  of  the  acid  being  diminished,  there  occurs  fer- 
mentation of  the  carbohydrates,  and  lactic,  acetic,  and 
butyric  acids  appear,  together  with  hydrogen  and  other 
gases.  These  acids  and  gases  give  rise  to  heartburn, 
waterbrash,  and  other  conditions  indicative  of  disordered 
digestion. 

C.  Intestinal  Digestion. 

The  small  intestine,  in  which  intestinal  digestion  takes 
place,  is  about  22  feet  long,  extending  from  the  stomach 
to  the  ileo-cscal  valve,  where  it  passes  into  the  large  in- 
testine. 

Coats  of  the  Intestiiie. — Like  the  stomach,  the  small  in- 
testine is  composed  of  four  coats  :  i,  serous  ;  2,  muscular; 
3,  submucous  ;  4,  mucous.  It  is  divided  into  three  por- 
tions :  [a),  duodenum  ;  {b),  jejunum  ;  {c),  ileum.  As  in  the 
stomach,  the  two  coats  which  have  physiological  interest 
are  the  muscular  and  the  mucoiis.  The  muscular  coat  is 
made  up  of  two  layers  :  an  external  or  longitudinal  and 
an  inner  or  circular. 


INTESTIA'AL   DIGESTION'. 


119 


Intestine,   laid  open   to  show  the  valvulae 

conniventes  (Brinton). 


VahndcB  Conniventes. — The  mucous  coat  of  the  intestine 
is  covered  by  a  single  layer  of  columnar  epithelium.  It 
is  arranged  in  folds  to 
which  the  name  "valvulae  f^.^^^'^"'- 
conniventes "  has  been 
given  (Fig.  lo).  These 
folds,  which  begin  about  i 
centimetres  below  the  py- 
lorus, are  present  through-  Fig.  lo.-Portion  of  the  Wall  of  the  Small 
out  the  length  of  the  small 
intestine,  excepting  in  the 
lower  part  of  the  ileum.  They  are  more  abundant  in 
the  upper  half  of  the  intestine,  where  they  have  been 
counted  to  the  number  of  six  hundred,  than  in  the  lower 
half,  where  only  two  hundred  and  fifty  have  been  found. 
These  folds  are  arranged  around  the  interior  of  the  in- 
testine at  right  angles  to  its  long  axis.  They  do  not 
completely  encircle  it  like  a  ring,  but  vary  in  length, 
some  extending  two-thirds  and  others  only  one-third  the 
distance  around.  The  widest  of  them  is  not  more  than 
half  an  inch  in  width,  projecting  into  the  calibre  of  the 
intestine  to  this  extent.  Each  fold  is  mucous  membrane, 
and  between  these  reduplications  of  mucous  membrane 
is  connective  tissue,  which  so  binds  the  folds  together 
that  even  in  the  condition  of  distention  the  valvulae  con- 
niventes are  not  obliterated,  as  is  the  case  with  the  rugae 
of  the  stomach.  By  means  of  these  foldings  the  extent 
of  the  mucous  membrane  is  greatly  increased  over  what 
it  would  be  did  it  simply  line  the  intestine. 

Villi. — Projecting  from  the  mucous  membrane  includ- 
ing the  valvulae  conniventes  are  the  "villi"  (Fig.  ii), 
which  are  so  numerous  as  to  give  to  it  a  velvety  appear- 
ance.   These  villi  are  prominences,  some  triangular,  some 


1 20 


HUMAN  PHYSIOLOGY. 


WPiE'"f:|-''l#--Wife^^^  are  intimately  connected  \ 

^■^Jip^lijl-iigplljl^^^  the  process  of  absorption, 


i^^P-"^:^ 


conical,  and  some  filiform  in  shape,  and  in  length  are  about 
i  mm.,  and  in  width  at  their  base  about  one-fourth  their 

length.  They  are  most  nu- 
merous in  the  duodenum  and 
the  jejunum,  although  present 
throughout  the  whole  extent 
of  the  small  intestine.  It  has 
been  estimated  that  there  are 
no  less  than  five  millions  of 
these  villi  in  an  intestine.   They 

with 

and 

their    further    description    will 

therefore  be  deferred  until  that 

subject  is  discussed. 

Bmnner's  Glands. — In  the 
submucous  coat  of  the  upper 
part  of  the  duodenum,  and,  to 
a  less  extent,  in  that  of  the 
lower  part  and  in  the  begin- 
K.y  ning  of  the  jejunum,,  are  certain 
glands  known  as  the  "  glands 
Fm.  xi.-verticai  Section  of  Duode-  ^^  grunner,"  or  the  duodenal 

num,  snowing  villi  (a)  ;   crypts  ol 

Lieberkuhn(/;),andBrunner's glands    glauds.         ThcSC     are     raCCmOSe 

(c)  in  the  submucosa  (j),  with  ducts       ,  ,  •       -i         ^       ^i  •        ^i 

{d):  muscuiaris  mucosa  (;«),  and  glands.  Similar  to  thosc  lu  the 

circular    muscular  coat  (/),  (Scho-    oeSOphagUS     aud      alsO     tO      tllC 

lobules  of  a  salivary  gland. 
They  discharge  through  ducts  which  open  upon  the 
surface  of  the  mucous  membrane  of  the  intestine.  Their 
secretion  is  mucus  having  a  slightly  alkaline  reaction, 
but  it  has  never  been  successfully  obtained  so  pure  as 
to  admit  of  its  being  analyzed.  These  glands  are  so 
few  in  number,  cornparatively,  that  their  product  cannot 


INTESTINAL   DIGESTION.  121 

be  very  abundant  nor  very  important  in  its  action  upon 
the  food,  although  a  ferment  has  been  described  as  one 
of  its  constituents  which  has  the  power  of  conv^erting 
maltose  into  glucose.  The  secretion  of  these  glands, 
together  with  that  of  the  follicles  of  Lieberkiihn,  con- 
stitutes the  intestinal  juice.  These  glands  are  inflamed 
and  ulcerate  whenever  the  body  is  burned  to  any  great 
extent. 

Follicles  of  Lieberkiihn. — The  follicles  or  crypts  of 
Lieberkuhn,  which  are  found  throughout  the  entire 
length  of  the  small  intestine,  are  tubular  glands  in  the 
mucous  membrane,  and  not  beneath  it,  as  is  the  case  with 
the  glands  of  Brunner.  Their  lining  is  a  layer  of  colum- 
nar epithelium.  Besides  these  tubular  glands  there  are 
solitary  glands  scattered  throughout  the  mucous  mem- 
brane of  the  intestine,  and  agminated  glands,  commonly 
known  as  "  Peyer's  patches,"  which  number  about  twenty- 
five,  and  which  are  most  numerous  in  the  ileum.  These 
glands  have  no  excretory  ducts,  but  they  produce  a  secre- 
tion which  probably  oozes  through  the  walls  of  the  glands 
and  contributes  something  to  the  intestinal  juice.  In 
typhoid  fever  Peyer's  patches  become  inflamed  and  often 
undergo  ulceration. 

Intestinal  Juice. — The  intestinal  juice,  "succus  en- 
tericus,"  is  the  product  of  all  the  glands,  but  the  follicles 
of  Lieberkuhn,  being  vastly  more  numerous,  contribute 
by  far  the  greater  part  of  this  fluid.  It  is  an  alkaline 
secretion  having  a  specific  gravity  of  loio,  and  contain- 
ing about  95  per  cent,  of  water,  salts,  and  at  least  one 
ferment,  invertin.  As  to  the  presence  of  other  ferments 
there  is  doubt. 

Action  of  Intestinal  Juice. — The  action  of  intestinal 
juice  upon  the  food  has  not  been  thoroughly  determined. 


122 


HUMAN  PHYSIOLOGY. 


The  property  which  it  possesses  in  the  most  marked 
degree  is  that  of  changing  cane-sugar  into  invert- 
sugar,  which,  as  will  be  remembered,  is  a  mixture  of 
Isevulose  and  dextrose.  This  inversion  is  due  to  the  fer- 
ment invertin.     The  intestinal  juice  also  converts  starch. 


Fig.  12. — Section  of  Lobule  of  a  Rabbit's  Liver,  in  which  the  blood  and  bile-capillaries 
have  been  injected  (after  Cadiat)  :  a,  intralobular  vein;  (5,  interlobular  veins;  c, 
biliary  canals  beginning  in  fine  capillaries. 


both  raw  and  cooked,  into  sugar.  Maltose  is  changed 
into  glucose,  and  the  viscid  secretion  of  Peyer's  patches 
brings  about  the  latter  change  very  quickly.    The  neutral 


INTESTINAL   DIGESTION. 


123 


fats  are  not  decomposed  by  intestinal  juice,  but  this  fluid, 
by  virtue  of  its  alkalinity,  does  emulsify  them.  Its  action 
on  proteids  is  not  determined,  some  experimenters  report- 
ing that  it  possesses  proteolytic  powers,  others  denying  it. 

From  the  above  considerations  the  intestinal  juice 
may  be  regarded  as  possessing  some  digestive  action 
upon  the  food-stuffs,  the  most  marked  of  which  action 
is  its  power  of  inversion.  It  is  not  an  abundant  secre- 
tion, and  perhaps  its  most  important  office  is  to  lubricate 
the  mucous  membrane  of  the  small  intestine. 

The  Bile. — The  bile  is  one  of  the  products  of  the  cells 


Fig.  13. — The  Liver:  i,  right  lobe  ;  2,  left  lobe;  3,  posterior  border;  4,  anterior  bor- 
der; 5,  lobus  quadratus  ;  6,  lobus  Spigelii  ;  7,  lobus  caudatiis;  8,  9,  longitudinal  fis- 
sure; 10,  transverse  fissure;  11,  portal  vein;  12,  hepatic  artery;  13,  ductus  com- 
munis choledochus;  14,  gall-badder  fissure;  15,  inferior  vena  cava  ;  16,  hepatic 
vein;  17,  round  ligament ;  18,  suspensory  or  broad  ligament. 


of  the  liver,  and  as  it  is  secreted  it  passes  into  the  gall- 
bladder through  the  hepatic  and  cystic  ducts,  where  it  is 
stored  until  needed  at  the  time  of  intestinal  digestion. 
Bile  when  discharged  from  the  gall-bladder  is  a  viscid  fluid, 
having  in  man  a  golden-brown  color,  a  specific  gravity  of 


124 


HUMAN  PHYSIOLOGY. 


1018,  and  an  alkaline  reaction.  Its  viscidity  is  due  to 
mucus,  which  is  not  present  when  the  bile  leaves  the 
liver,  but  which  is  added  to  it  while  it  is  stored  in  the 


Qu  y^('<i^^^rr<. 


Fig.  14. — Section  of  the  Liver  of  the  Newt,  showing  the  bile-ducts  injected,  forming  a 
network  of  fine  capillaries  around  the  liver-cells,  the  outlines  and  nuclei  of  which 
can  be  seen. 

gall-bladder,  being  secreted  by  the  mucous  membrane 
lining  that  organ. 

The  quantity  of  human  bile  daily  secreted   is  about 
1500  cc,  and  its  composition  is — 

Water -86.  per  cent. 

Biliary  salts 9.       " 

Cholesterin 0.3     " 

Mucus  and  coloring  matters  ...     3.       " 
Salts  and  other  ingredients     .    .    .     1.7     " 

100. 


The  ingredients  of  the  bile  have  already  been  discussed 
in  the  section  treating  of  Physiological  Chemistry,  and 
the  offices  of  this  fluid  will  be  considered  later. 

Pancreatic  Juice. — The  pancreatic  juice  is  the  product 
of  the  pancreas,  and  is  discharged  into  the  duodenum  at 


INTESTINAL   DIGESTION.  I  25 

about  its  middle,  through  the  pancreatic  duct — or  ducts 
more  properly,  as  there  are  usually  two.  One  of  these, 
the  main  duct,  discharges  by  an  opening  common  to  it 
and  the  common  bile-duct.  During  the  intervals  of  di- 
gestion no  pancreatic  juice  flows  into  the  intestine,  but 
during  stomach  digestion  the  flow  begins,  even  before 
any  food  has  passed  from  the  stomach  into  the  duo- 
denum. It  is  a  viscid  fluid,  alkaline  in  reaction,  having 
a  high  specific  gravity.  The  quantity  secreted  daily  is 
variously  estimated,  some  placing  it  at  150  cc,  others 
at  a  much  higher  figure.  The  composition  of  pancreatic 
juice  (dog)  is  as  follows: 

Water 90  per  cent. 

Organic  matter  (including  albu- 
min and  ferments) 9        " 

Salts  (sodium  carbonate,  sodium 
chloride,  potassium  chloride, 
calcium  phosphate)      ....         i        " 

100 

Pancreatic  Ferments. — Special  interest  attaches  to  the 
pancreatic  ferments,  of  which  there  are  three — amylopsin, 
steapsin,  and  trypsin. 

Amylopsin  is  a  diastatic  or  amylolytic  ferment,  and  is 
sometimes  spoken  of  as  "  pancreatic  diastase."  It  is  not 
produced  in  the  human  subject  until  one  month  after 
birth.  It  converts  both  raw  and  cooked  starch  into 
maltose  and  some  dextrose. 

Steapsin  is  a  lipolytic  or  fat-splitting  ferment.  The 
fatty  acids  unite  with  the  carbonate  of  soda  of  the  pan- 
creatic juice,  forming  soaps,  so  that  there  is  an  actual 
process  of  saponification  taking  place  in  the  intestines. 


126  HUMAN  PHYSIOLOGY. 

Trypsin  is  a  proteolytic  ferment  having  the  power  to 
change  the  proteids,  which  have  not  already  been  pep- 
tonized by  the  gastric  juice,  into  peptone,  and  also  of 
changing  in  the  same  way  the  acid-albumins  and  albu- 
moses,  the  partial  products  of  stomach  digestion.  Tryp- 
■sinogen  is  first  formed  by  the  pancreas,  and  this  is  later 
changed  into  trypsin.  The  action  of  trypsin  is  in  some 
respects  like  that  of  pepsin,  but  in  other  respects  differs 
from  it.  Thus  pepsin  requires  the  presence  of  an  acid 
reaction,  while  trypsin  acts  when  the  reaction  is  alkaline 
or  neutral,  the  most  energetic  action  being  when  the 
alkali,  carbonate  of  soda,  is  present  to  the  amount  of 
from  0.3  to  0.4  per  cent.  Mineral  acids  prevent  the  action 
of  the  ferment,  but  lactic  and  other  organic  acids  do  not 
as  seriously  interfere  with  it.  It  has  been  noted  that 
salicylic  acid  in  large  quantities  will  inhibit  its  action. 
In  the  process  of  pepsin-digestion  an  acid-albumin  is 
first  formed;  in  trypsin-digestion  the  first  product  is  an 
alkali-albumin.  By  the  further  action  of  the  enzyme 
hemi-  and  anti-albumose  are  formed,  and  still  later  hemi- 
and  anti-peptones.  To  distinguish  the  product  of  the 
action  of  trypsin  from  that  of  pepsin  some  writers  speak 
of  the  former  as  "  tryptone."  The  hemi-peptones  may, 
by  the  continued  action  of  the  trypsin,  be  decomposed 
into  leucin  and  tyrosin.  This  power  is  not  possessed  by 
pepsin.  It  may,  perhaps,  be  questioned  whether  this 
formation  of  leucin  and  tyrosin  ordinarily  takes  place 
during  pancreatic  digestion,  as  it  requires  some  time  for 
its  accomplishment,  and  the  peptones  may  have  been 
absorbed  before  this  change  can  take  place ;  but  it  un- 
doubtedly does  occur  when  the  proteids  have  been  taken 
in  in  excess  of  the  demands  of  the  body.  There  is  doubt- 
less a  rennet-ferment  in  the  pancreatic  juice,  but  it  prob- 


INTESTINAL   DIGESTION.  12/ 

ably  is  rarely  called  upon  to  exert  its  specific  action,  as 
the  casein  of  milk  is  thoroughly  coagulated  before  enter- 
ing the  intestine  by  the  ferment  of  the  gastric  juice. 

After  the  above  consideration  of  the  intestinal  fluids 
we  are  in  a  position  to  understand  the  process  of  intes- 
tinal digestion  as  a  whole.  As  the  chyme  leaves  the 
stomach  its  reaction  is  markedly  acid,  and  unless  this 
acidity  is  overcome  the  ferments  of  the  intestine,  hav- 
ing no  power  in  acid  media,  can  exert  no  action  upon 
the  food.  It  is  essential,  therefore,  that  this  acidity  should 
be  neutralized.  The  presence  of  the  chyme  in  the  small 
intestine,  causes  through  nervous  agency,  the  gall-blad- 
der to  empty  itself  of  the  contained  bile,  which  is  dis- 
charged through  the  common  bile-duct  into  the  duo- 
denum. The  action  of  the  bile  on  the  chyme  is  such  as 
to  cause  the  peptones  and  acid-albumins  to  be  precip- 
itated, and  with  them  the  pepsin,  so  that  all  further  action 
of  this  ferment  is  prevented.  At  the  time  the  discharge 
of  bile  takes  place  into  the  intestine  the  secretions  of  the 
glands,  which  have  just  been  studied,  are  also  poured 
out,  and  begin  to  exercise  the  characteristic  properties 
already  mentioned — the  conversion  of  starch  into  sugar, 
of  proteids  into  peptones,  and  the  saponification  of  a  part 
of  the  fat.  In  addition  to  this  action  there  is  an  emulsi- 
fication  of  so  much  of  the  fat  as  is  not  saponified.  This 
does  not  seem  to  be  due  to  any  special  enzyme,  but  is 
attributable  to  the  alkalinity  of  the  fluids  and  the  pres- 
ence of  proteids  and  soap.  If  the  interior  of  the 
small  intestine  were  examined  at  this  stage  of  digestion, 
its  mucous  membrane  would  be  seen  covered  by  a  layer 
of  material  much  resembling  cream. 

The  bile,  then,  so  far  as  its  influence  in  digestion  is 
concerned,  has  for  its  special  purposes  the  termination 


128  HUMAN  PHYSIOLOGY. 

of  the  digestion  taking  place  in  the  stomach  and  the 
preparation  of  the  food  for  intestinal  digestion.  It  also 
stimulates  the  muscular  coat  of  the  small  intestine  to 
more  efficient  action,  thus  materially  aiding  in  propelling 
the  food  along  this  canal,  and  in  bringing  it  thereby  into 
contact  with  the  secretions  concerned  in  digestion.  This 
muscular  action  is  of  importance  also  in  the  process  of 
absorption.  Bile  aids  also  in  emulsifying  the  fats,  although 
the  principal  factor  in  that  process  is  doubtless  the  pan- 
creatic juice.  The  absorption  of  the  fats  after  being 
emulsified  is  materially  aided  by  the  bile.  Some  claim 
has  been  made  for  its  antiseptic  properties,  but  the  pres- 
ence of  bacteria  in  it  would  seem  to  controvert  this.  It 
is,  however,  a  noteworthy  fact  that  when  a  biliary  fistula 
is  made,  and  the  bile,  instead  of  pursuing  its  normal  route 
into  the  intestine,  is  withdrawn  directly  from  the  gall- 
bladder, the  faeces  become  very  offensive.  The  bile  prob- 
ably prevents  the  excessive  formation  of  those  ingredients 
which  give  the  characteristic  odor  to  the  faeces,  and  these 
are  produced  to  a  greater  degree  when  the  discharge  of 
bile  into  the  small  intestine  is  interfered  with.  The  bile 
is  also,  in  part,  an  excrementitious  fluid,  as  is  shown  by 
the  blood-poisoning  which  occurs  when  the  bile  is  not 
normally  formed  by  the  liver,  or  when,  after  having  been 
formed,  it  is  reabsorbed. 

After  the  bile  has  performed  its  part  in  the  intestine  it 
undergoes  disintegration.  The  mucin,  cholesterin,  and 
part  of  the  coloring  matter  in  the  form  of  hydrobilirubin 
pass  off  into  the  faeces.  A  part  of  the  coloring  matter  is 
excreted  in  the  urine  as  urobilin.  The  biliary  salts  are 
reabsorbed  and  enter  the  blood. 

All  the  food-stuffs  requiring  it,  excepting  the  fats, 
having   been    made   diffusible  by  the  various   digestive 


INTESTIXAL   DIGESTION.  1 29 

processes,  the  process  by  which  they  are  rendered  avail- 
able for  nutrition  may  now  be  studied ;  that  is,  the  pro- 
cess of  absorption,  for,  as  has  been  stated,  until  they 
reach  the  blood  they  are  of  no  use  to  the  economy  of 
the  body. 

TJie  Large  Intestine. — Before  taking  up  the  subject  of 
absorption  the  functions  of  the  large  intestine  will  be 
considered. 

The  innutritious  portions  of  the  food  are  carried  along 
by  the  action  of  the  muscular  coat  of  the  small  intestine 
into  the  large  intestine,  together  with  those  bile-constit- 
uents which  are  not  reabsorbed.  Here  they  are  added 
to  by  the  secretion  of  the  mucous-membrane  glands, 
some  of  which  closely  resemble  the  follicles  of  Lieber- 
kiihn.  This  secretion  is  an  alkaline  fluid,  but  its  diges- 
tive power,  if  it  possess  any,  is  unimportant.  Although 
this  fluid  is  alkaline,  still  the  contents  of  the  large  intes- 
tine are  acid,  owing  to  the  fermentative  process. 

While  the  large  intestine  has  no  digestive  power,  it 
has  considerable  power  of  absorption.  This  absorptive 
power  is  constantly  being  exercised  by  the  withdrawal 
of  the  liquid  portion  of  the  intestinal  contents  as  they 
pass  along,  making  them  more  and  more  consistent  until 
they  are  discharged  at  the  anus.  This  power  possessed 
by  the  large  intestine  is  made  use  of  in  certain  diseases 
of  the  .stomach,  in  which  diseases  that  organ  is  unable 
to  perform  its  function,  when  by  means  of  nutrient 
enemata,  skilfully  administered,  life  may  be  maintained 
for  a  long  time.  In  a  case  of  circumscribed  peritonitis 
from  perforated  gastric  ulcer  a  female  patient  was  nour- 
ished on  the  following  rectal  enema  for  ninety-four 
days,  during  which  time  she  lost  but  2700  grammes 
in  weight: 
9 


130  HUMAN  PHYSIOLOGY. 

Lean  beef 300  grammes. 

Pancreas 150         " 

These  were  well  rubbed  up  in  a  mortar  and  strained,  and 
then  there  were  added  : 

Water q.  s. 

Carbonate  of  soda 5  grammes. 

Fresh  ox-gall 25         " 

This  sufficed  for  four  enemata  a  day  when  diluted  with 
a  sufficient  amount  of  tepid  water. 


Fig.  15. — Microscopical  Constituents  of  the  Stools  (partly  from  Jaksch)  :  a,  vegetable 
fragments  ;  b,  muscular  fibres  ;  c,  white  blood-corpuscles  ;  d,  saccharomyces ;  e, 
micro-organisms ;  y,  crystals  of  triple  phosphate;  g,  fatty-acid  crystals. 


Fig.  16. — Monads  from  the  Faeces  (Jaksch)  :  a,  tricomonas  intestinalis  ;  b,  cercomonas 
intestinalis ;  c,  amoeba  coli ;  d,  paramsecium  coli ;  e,  living  monads ;  f,  dead  monads. 


ABSORPTION.  131 

The  contents  of  the  large  intestine  are  called  the 
"faeces"  (Figs.  15,  16),  and  are  made  up  of  useless  por- 
tions of  the  food,  of  certain  ingredients  of  the  bile,  mu- 
cus.'stercorin,  skatol,  indol,  and  other  excretory  products, 
and  some  salts.  Nitrogen,  carbon  dioxide,  and  car- 
buretted  hydrogen  are  almost  always  found,  and  some- 
times hydrogen  and  hydrogen  monosulphide.  These 
gases  doubtless  are  the  result  of  decomposition  of  the 
food.  The  amount  of  fecal  matter  daily  evacuated  by 
an  adult  is  about  160  grammes,  74  per  cent,  of  which 
is  water. 

2,  Absorption. 

Absorption  takes  place  in  the  mouth,  in  the  stomach, 
and  in  the  small  intestine.  The  epithelium  lining  the 
mouth  is  not  well  adapted  for  absorption,  yet  that  this 
does  occur  is  proved  by  the  fact  that  cyanide  of  potas- 
sium taken  into,  and  remaining  in,  the  mouth  will  cause 
death.  As  has  been  noted,  the  amount  of  absorption 
of  food  taking  place  in  the  mouth  is  very  small,  while 
that  taking  place  in  the  stomach  is  much  greater.  Salts, 
dextrose,  and  some  peptones  here  find  their  way  into  the 
blood  through  the  walls  of  the  veins,  and  it  is  a  well- 
known  fact  that  some  poisons  are  absorbed  from  the 
stomach.  It  has  been  claimed  that  when  milk  is  taken 
in  large  amount  some  of  its  fatty  portions  are  absorbed 
by  the  vessels  of  the  stomach.  But  to  the  small  in- 
testine must  be  referred  the  accomplishment  of  the 
greatest  part  in  absorption  ;  for  here  there  is  not  only 
a  very  large  area  of  absorbing  surface,  it  having  been 
estimated  to  be  10  square  metres,  but  here  also  are  those 
structures  which  are  especially  adapted  to  perform  this 
function — namely,  the  villi. 


132 


HUMAN  PHYSIOLOGY. 


Structure  of  the  Villi. — The  general  characteristics 
of  the  villi  and  their  enormous  number  Jiave  been 
already  referred  to.  Each  villus  (Fig.  17)  is  composed  of 
a  single  layer  of  columnar  epithe- 
lium, lying  upon  a  basement  mem- 
brane, beneath  which  is  a  plexus 
of  capillary  blood-vessels.  Interior 
to  this  are  non-striated  muscular 
fibres  which  cover  a  lacteal.  Be- 
tween the  basement  membrane  and 
the  contained  structures,  and  inter- 
twined with  them,  is  a  network  of 
connective  tissue  in  which  are  cells, 
including  leucocytes,  and  which  is 
called  "  lymphoid  tissue."  The 
lacteal,  which  is  in  the  centre  of 
the  villus,  is  a  lymphatic  vessel ; 
that  in  some  villi  is  single,  and  in 
some  double,  and  begins  by  a  blind 
extremity.  The  connection  be- 
tween the  lacteal  and  the  columnar 
epithelium  is  made  by  the  network 
spoken  of  above. 

The    lacteals    are    so   called   be- 
cause during  the  period  of  absorp- 
FiG.  i7.-viiius.  with  the  ca-   tiou  of  the  digested  food  they  con- 
piUaries  injected,  showing   ^-^jj^  ^  material  rcscmbling  milk  in 

their  close   relation   to   epi- 
thelium, some  of  the  cells    appcaraucc,  this  material  being  the 
of  which  are  distended  with      ,  ^       ^j^^  kctcals  In  reality  are 

mucus  (Cadiat).  ''  •' 

lymphatic  vessels,  and  in  the  inter- 
vals of  digestion  they  contain  lymph  as  do  other  lym- 
phatics. When  containing  chyle,  the  lacteals,  as  they 
course  through  the  mesentery,  appear  like  minute  white 


ABSORPTION.  133 

threads,  by  reason  of  the  milky  fluid   showing  through 
their  transparent  walls.      At  other  times,  when  carrying 


Fig.  18. — Diagram  showing  the  Course  of  the  Main  Trunks  of  the  Absorbent  System  : 
the  lymphatics  of  lower  extremities  (d)  meet  the  lacteals  of  intestines  (lac)  at  the 
receptaculum  chyli  (rc),  where  the  thoracic  duct  begins.  The  superficial  vessels  are 
shown  in  the  diagram  on  the  right  arm  and  leg  (s),  and  the  deeper  ones  on  the  left 
arm  (d).  The  glands  are  here  and  there  shown  in  groups.  The  small  right  duct 
opens  into  the  veins  on  the  right  side.  The  thoracic  duct  opens  into  the  union  of 
the  great  veins  of  the  left  side  of  the  neck  (t). 

lymph  alone,  they  cannot  be  distinguished  from  the  sur- 
rounding tissue. 

Lymph. — Lymph  is  the  fluid  which  remains  after  the 
tissues  have  taken  from  the  blood  the  materials  needed 
for  their  nutrition.  This  fluid  has  still  nutritive  proper- 
ties which  are  too  valuable  to  be  lost ;  hence  provision 
is  made  for  its  return  to  the  circulation.  The  vessels  by 
which  it  returns  are  the  lymphatics.  The  following 
table  gives  the  composition  of  human  lymph: 


134 


HUMAN  PHYSIOLOGY. 


Water 9399 

Fibrin 06 

Albuminous  (caseous)  matter  (with 
earthy  phosphates  and  traces   of 

iron) 4.27 

Fatty  matter 38 

Hydro-alcohohc  extract  (containing 
sugar,  and  leaving  after  incinera- 
tion sodium  chloride,  with  sodium 
phosphate  and  carbonate)  .    .    .    ,     1.30 

100.00 

Lymph  contains  the  same  ingredients  as  the  blood 
from  which  it  is  derived,  except  that  the  red  corpuscles 
are  absent.  The  proportion,  however,  in  which  the 
ingredients  exist  is    not  the  same. 

Chyle. — If  the  composition  of  the  ch\-le  be  examined 
it  will  be  found  that  chyle  contains  more  albuminous 
matter,  more  fibrin,  and  very  much  more  fatty  matter 
than  the  l}'mph.  The  following  table  shows  the  com- 
position of  chyle  from  a  donkey : 

W'ater  


Albuminous  matter 
Fibrinous  matter  . 
Fatt}"  matter    .    .    . 

Salts 

Extractive  matter  . 


90.24 

3-51 

•37 

3.60 

•71 
1.57 


100.00 

The  efficient  agents  in  absorption  are  the  blood-ves- 
sels and  the  lacteals.  All  the  blood  from  the  stomach 
and  the  small  intestine  passes  into  the  portal  circulation 
of  the  liver.  B)'  this  channel  most  of  the  peptones  find 
their  way  into  the  circulation,  as  do  also  the  salts  and 


ABSORPTION.  135 

sugar,  as  well  as  some  fat.  By  the  lacteals  the  greater 
part  of  the  emulsified  fat  is  absorbed,  as  are  also  some  of 
the  peptones  and  some  of  the  sugar.  By  the  lacteals  a 
portion  of  the  water  taken  in  as  drink  is  absorbed,  al- 
though the  greater  part  of  the  latter  is  taken  up  by  the 
blood-vessels.  In  general  it  may  be  said  that  all  the 
products  of  digestion  are  absorbed  by  each  of  the  sets 
of  absorbents,  but  the  lacteals  absorb  most  of  the  fat, 
and  the  blood-vessels  most  of  the  sugar  and  peptones. 

Absorptio7t  of  Fat. — Much  interest  attaches  to  the 
method  by  which  the  fatty  portion  of  the  food  reaches 
the  lacteals.  It  has  been  seen  that  the  fat  is  emulsified 
in  the  small  intestine;  that  is,  broken  up  into  an  exceed- 
ingly fine  state  of  subdivision — so  fine,  indeed,  that  the 
size  of  the  globules  is  from  i  to  2  m.mm.  Although  the 
statement  that  these  globules  pass  into  and  through  the 
epithelium  of  the  villi  has  been  contradicted,  the  weight 
of  evidence  at  the  present  time  seems  to  be  in  favor  of 
this  explanation.  It  is  not  to  be  supposed  that  the  fat 
or  other  substances  absorbed  by  the  villi  passes  into  them 
by  a  sort  of  filtering  process ;  there  is  undoubtedly  a 
selective  power  exercised  by  the  epithelial  covering. 
From  the  epithelium  through  the  lymphoid  tissue  to 
the  lacteal  is  a  continuous  path  which  is  followed  b\'  the 
fat.  The  presence  of  the  bile  undoubtedly  aids  in  the 
process,  as  experiment  shows  that  membranes  moistened 
with  bile  permit  substances  the  more  readily  to  pass 
through  them.  Some  fat,  probably  a  very  small  portion, 
is  also  absorbed  as  soap. 

The  changes  which  the  products  of  digestion  undergo 
after  being  absorbed  are  exceedingly  obscure,  very  little 
being  known  of  them.  The  sugar  which  is  the  product 
of  the  changes  that  have  taken  place  in  the  carbohy- 


136  HUMAN  PHYSIOLOGY. 

drates  is  dehydrated  by  the  liver-cells,  and  is  deposited 
in  them  as  glycogen.  This  glycogen  is  gradually  re- 
converted by  the  liver-cells  into  sugar  and  is  taken  up 
by  the  blood.  It  is  carried  by  the  blood  to  the  muscles, 
where  it  is  utilized  in  their  activities,  being  broken  up 
ultimately  into  carbon  dioxide  and  water,  in  which  form 
it  is  eliminated  from  the  body.  This  production  of  sugar 
by  the  liver  is  its  glycogenic  function.  The  peptones 
are  converted  into  albumin  while  passing  through  the 
mucous  membrane,  probably  in  the  epithelium,  and  in 
that  condition  are  taken  up  by  the  blood.  The  fat  and 
other  materials  taken  up  by  the  lacteals  find  their  way 
into  the  thoracic  duct,  and  thence  into  the  venous 
system. 

It  is  deemed  important  to  direct  attention  to  the  fact 
that  at  the  present  time  more  regard  is  paid  by  author- 
ities to  the  selective  power  of  the  epithelium  of  the  villi 
as  absorbing  agents  than  to  the  older  idea  of  osmosis. 

Blood. — The  office  of  blood  is  twofold:  i.  It  carries 
to  the  tissues  of  the  body  the  materials  which  they  need 
for  their  nourishment,  and,  in  the  case  of  glands,  for 
their  secretion ;  and  2.  It  takes  from  the  tissues  the 
materials  which  result  from  their  destructive  metabolism 
— waste  materials — which  it  carries  to  those  structures 
whose  office  it  is  to  eliminate  them,  as,  for  instance,  urea 
to  the  kidneys.  The  blood  may  be  likened  to  a  river 
which  bears  to  the  inhabitants  along  its  banks  their  daily 
food,  and  into  which  at  the  same  time  their  waste  is  dis- 
charged and  carried  to  the  sea. 

Physical  Properties  of  Blood. — Blood  is  in  general  red 
in  color  and  alkaline  in  reaction,  and  has  a  specific  grav- 
ity of  1055.  The  specific  gravity  of  the  corpuscles  is 
1 105,  that  of  the  plasma  1027. 


ABSORPTION.  137 

Color  of  Blood. — Although  generally  blood  is  said  to 
be  red,  still  this  color  is  subject  to  considerable  varia- 
tion. Thus,  venous  blood  is  variously  described  as 
bluish-red,  reddish-black,  deep  purple,  dark  purplish- 
red,  dark  blue,  and  dark  purple,  while  arterial  blood  is 
a  bright  scarlet.  The  color  of  blood  depends  on  haemo- 
globin or  its  derivatives.  In  the  blood  of  an  animal 
thafe  has  been  suffocated,  where  the  purplish  or  blackish 
color  is  most  pronounced,  the  coloring  matter  is  almost 
entirely  haemoglobin,  while  in  arterial  blood  the  oxyha^mo- 
globin  predominates,  and  in  ordinary  venous  blood  there 
is  a  mixture  of  haemoglobin  and  oxyhaemoglobin. 

Reaction  of  Blood. — The  alkalinity  of  blood  is  a  prop- 
erty essential  to  life.  It  depends  upon  the  presence  of 
disodic  phosphate  and  sodium  bicarbonate.  It  is  said 
that  the  blood  becomes  acid  immediately  before  death 
in  cases  of  cholera. 

Odor  of  Blood. — Blood  has  an  odor  which  is  said  to 
be  characteristic  of  the  species  of  animal  from  which  it 
is  taken.  This  odor  is  usually  very  slight,  but  it  may  be 
brought  out  by  the  addition  of  sulphuric  acid. 

Taste  of  Blood. — The  sodium  chloride  which  blood 
contains  gives  to  it  a  salty  taste. 

Quantity  of  Blood. — The  amount  of  blood  in  the  body 
of  a  human  adult  is  about  one-thirteenth  of  his  weight; 
some  authorities  state  one-eighth,  and  others  one-four- 
teenth. In  a  new-born  child  it  is  about  one-nineteenth. 
During  the  latter  half  of  the  period  of  pregnancy  it  is 
increased,  and  it  is  also  increased  during  digestion. 

Distribution  of  Blood. — The  distribution  of  the  blood 
in  the  body  is  as  follows  : 

In  the  heart,  lungs,  and  great  blood-ves.sels,  one-fourth. 

In  the  skeletal  muscles,  one-fourth. 


138  HUMAN  PHYSIOLOGY. 

In  the  liver,  one-fourth. 

In  the  rest  of  the  body,  one-fourth. 

Temperature  of  Blood. — The  temperature  of  blood 
varies  greatly  in  the  different  parts  of  the  circulatory 
apparatus.  The  mean  temperature  may  be  stated  as  39° 
G. ;  that  of  the  superior  vena  cava,  36.78°  C. ;  the  right 
side  of  the  heart,  38.8°  C;  the  leftside  of  the  heart,  38.6° 
C. ;  the  aorta,  38.7°  C. ;  the  portal  vein,  39.9°  C. ;  the 
hepatic  vein,  41.3°  C.  The  temperature  of  the  blood  in 
the  hepatic  vein  is  the  highest  in  the  body,  and  it  varies 
from  39.5°  C.  at  the  beginning  of  digestion  to  41.3°  C.  at 
the  time  when  the  process  is  the  most  active.  The  blood 
in  the  right  side  of  the  heart  is  made  warmer  by  its 
proximity  to  the  liver,  while  in  its  circulation  through 
the  lungs  it  loses  heat,  and  is  therefore  cooler  in  the  left 
side  of  the  heart.  In  the  portions  of  the  body  exposed 
to  the  air,  as  in  the  skin,  the  temperature  of  the  blood  is 
doubtless  as  low  as  36.5°  C. 

Microscopical  Structure  of  the  Blood. — When  examined 
by  the  microscope  the  blood  is  seen  to  be  composed  of 
a  fluid  portion,  plasma  or  liquor  sanguinis,  in  which  are 
suspended  bodies  called  "  corpuscles."  The  plasma 
is  a  straw-colored  fluid,  the  color  being  due  to  lutein, 
whose  chemical  composition  will  be  hereafter  dis- 
cussed. 

Blood-corpuscles  are  of  three  varieties:  (i)  Red  cor- 
puscles ;  (2)  white  corpuscles ;  and  (3)  plaques. 

Red  corpuscles  in  human  blood  are  circular,  bicon- 
cave, non-nucleated  disks,  having  an  average  diam- 
eter of  J.']  m.mm.,  some  of  them  being  as  small  as  4.5 
m.mm.,.  while  others  are  9  m.mm.  In  chronic  anaemic 
conditions  some  have  been  found  as  large  as  14  m.mm., 
and  others  as  small  as  2.2  m.mm. 


ABSORPTION.  139 

Number  of  Blood-corpuscles. — The  number  of  red  cor- 
puscles in  a  millimetre  of  the  blood  of  a  male  adult 
has  been  reckoned  at  5,000,000;  in  that  of  a  female, 
4,500,000.     In  anaemia  this  number  has  been  reduced 


Fig.  19. — Blood-corpuscles    (Eberth  and  Schimmelbiisch)  :   a,  blood-plaques  or  third 
corpuscles  ;  b,  red  corpuscles;  c,  white  corpuscles. 

to  1,000,000.  In  all  the  blood  of  the  body  in  health  their 
number  is  consequently  enormous. 

Color  of  Red  Corpuscles. — A  single  corpuscle  is  of  a 
yellowish  or  amber  color,  and  the  red  color  of  the  blood 
only  appears  when  the  corpuscles  are  in  thick  layers  or 
in  masses.  They  are  exceedingly  flexible,  as  may  readily 
be  seen  by  watching  them  in  the  circulation  of  the  web 
of  a  frog's  foot.  At  times  they  will  be  so  stretched  out 
as  to  pass  through  a  vessel  whose  diameter  is  smaller 
than  is  theirs  when  in  a  circular  shape,  or  sometimes 
they  may  be  seen  bent  over  the  projection  made  by 
the  junction  of  two  vessels,  one  portion  being  within 
each,  until,  one  current  being  the  stronger,  they  are 
carried  into  it,  resuming  their  circular  shape  as  soon  as 
that  is  possible. 

Structure  of  Red  Corpuscles. — The  red  corpuscles  are 
composed  of  a  substance  called  the  "stroma"  and  of  the 
coloring  matter.  Some  of  the  constituents  of  the  stroma 
have  been  determined.  These  constituents  are  lecithin, 
cholesterin,  and  cell-globulin.  Potassium,  sodium,  phos- 
phoric acid,  and  chlorine  have  also  been  obtained.  The 
coloring  matter  has  already  been  spoken  of     During  a 


140  HUMAN  PHYSIOLOGY. 

portion  of  foetal  life  the  human  red  blood-corpuscle  has 
a  nucleus,  but  this  disappears  at  about  the  fourth  month, 
and  it  is  wanting  in  the  adult. 

Development  of  Red  Blood-corpuscles. — The  corpuscles 
are  developed  in  the  area  vasculosa  of  the  embryo  from  the 
cells  which  result  from  the  segmentation  of  the  vitellus. 
These  divide,  and  thus  form  new  corpuscles.  They  are 
formed  also  in  the  liver,  in  the  spleen,  and  in  the  red  mar- 
row of  bones,  being  found  in  the  red  marrow  after  birth. 
This  red  marrow  occurs  in  the  bones  of  the  skull  and 
in  the  trunk.  In  the  bones  of  the  extremities  the  mar- 
row is  yellow  and  is  largely  fatty.  If  any  red  marrow 
be  found  in  the  bones,  it  is  in  their  heads.  It  is  said  that 
after  severe  hemorrhages,  when  the  production  of  red 
corpuscles  is  very  active,  this  yellow  marrow  becomes 
red  and  produces  red  corpuscles.  Some  have  claimed 
that  they  are  also  formed  from  white  corpuscles,  but  this 
claim  is  doubtful. 

Destniction  of  Red  Blood-corpuscles. — The  duration  of  a 
red  blood-corpuscle  is  undetermined,  but  it  is  doubtless 
limited.  Some  authorities  place  its  life  at  from  three 
to  four  weeks.  Old  corpuscles  constantly  undergo  dis- 
integration and  new  ones  appear.  The  fact  that  fewer 
corpuscles  are  found  in  the  blood  of  the  hepatic  than  in 
that  of  the  portal  vein,  and  the  additional  fact  that  biliary 
pigment  is  formed  from  the  coloring  matter  of  the  blood, 
indicate  that  in  the  liver  a  part,  at  least,  of  these  destruc- 
tive changes  takes  place.  These  same  changes  take  place 
also  in  the  spleen.  If,  as  there  is  reason  to  believe,  the 
pigment  of  the  bile  and  the  urine  be  formed  from  that  of 
the  blood,  the  number  of  the  corpuscles  daily  destroyed 
must  be  very  great. 

Function  of  Red  Blood-corpuscles. — The  red  corpuscles 


ABSORPTION.  141 

are  the  carriers  of  oxygen  to  the  tissues,  without  which 
oxygen  they  could  exist  but  for  a  short  time.  The 
blood  can  absorb  at  least  ten  times  as  much  of  this  gas 
as  can  the  same  amount  of  water,  and  this  absorption 
is  due  principally  to  the  affinity  which  the  haemoglobin 
has  for  it.  While  oxygen  is  mainly  in  the  corpuscles, 
carbon  dioxide  is  in  the  plasma. 

WJilte  blood-corpuscles  are  sometimes  spoken  of  as 
"  colorless  corpuscles,"  and  sometimes  as  "  leucocytes." 
The  last  term  is,  perhaps,  the  best,  as  under  it  are  in- 
cluded cells  which  are  found  in  lymph,  chyle,  pus,  con- 
nective tissue,  and  elsewhere,  and  which  cannot  be 
distinguished  from  those  found  in  the  blood.  The  size 
of  white  corpuscles  is  variable,  from  4  to  13  m. mm.,  aver- 
aging perhaps  10  m.mm.  The  shape  of  these  corpuscles  is 
said  to  be  spherical,  but  by  virtue  of  their  power  of 
amoeboid  movement  their  form  is  constantly  changing. 
They  consist  of  masses  of  protoplasm  containing  a 
nucleus,  and  sometimes  more  than  one.  Their  niiinber  is 
commonly  said  to  be,  compared  with  the  red  corpuscles, 
as  I  to  350  or  I  to  750,  but  these  figures  are  of  but  little 
value,  so  greatly  does  the  proportion  vary  under  differ- 
ent conditions  and  in  different  portions  of  the  circulatory 
apparatus.  Thus,  after  eating  this  proportion  is  much 
increased,  as  is  also  the  case  after  the  loss  of  blood, 
during  suppurative  processes,  and  after  the  use  of  bitter 
tonics;  while  in  a  state  of  hunger  or  deficient  nourish- 
ment it  is  diminished.  In  the  splenic  vein  the  propor- 
tion has  been  found  to  be  as  i  to  60 ;  in  the  splenic 
artery,  i  to  2260;  hepatic  vein,  i  to  170;  and  portal 
vein,  I  to  740.  As  a  rule,  white  corpuscles  are  more 
numerous  in  the  veins  than  in  the  arteries.  The  great 
difficulty  encountered    in   attempting   to    ascertain  the 


142 


HUMAN  PHYSIOLOGY. 


number  of  white  corpuscles  is  due  to  the  fact  that  in 
the  shedding  of  blood  large  numbers  disappear.  One 
authority  estimates  that  only  one-tenth  of  the  number 
that  existed  in  the  blood  when  it  was  circulating  remains 
after  it  has  left  the  blood-vessel. 

Composition  of  White  Blood-corpuscles. — White  cor- 
puscles contain  myosin,  serum-globulin,  glycogen,  leci- 
thin, cholesterin,  nuclein,  salts  of  sodium,  potassium, 
calcium,  and  magnesium.  Besides  these  ingredients  they 
contain  a  zymogen  which  produces  fibrin-ferment. 

Functio7i  of  White  Blood-corpuscles. — But  little  is 
known  of  the  function  of  the  white  corpuscles  of  the 
blood,  except  that  concerned  in  the  process  of  coagu- 


FiG.  20.— Changes  in  the  Leucocyte  of  a  Frog  during  ten  minutes  {Am.  Text-book  of 

Stirgery). 

lation.  As  already  stated,  it  is  doubtful  if  they  have 
anything  to  do  with  the  formation  of  the  red  cor- 
puscles. 

Blood-plaques  are  known  also  as  "  blood-plates  "  and 


ABSORPTION.  143 

"  haematoblasts."  The  latter  name  has  been  given  them 
because  they  are  regarded  by  some  authorities  as  an  early 
stage  in  the  development  of  the  red  corpuscles.  Blood- 
plaques  are  round  or  oval  in  shape  and  are  colorless. 
Their  size  is  very  variable,  averaging  perhaps  3  m.mm. 
Their  number,  compared  with  the  red  corpuscles,  is  as  i  to 
25  or  180,000  to  250,000  per  cubic  millimetre  of  blood. 

T\v&  function  of  blood-plaques  is  undetermined. 

Blood-plasma  and  liquor  sanguinis  are  synonymous 
terms,  but  serum,  which  is  often  used  as  interchangeable 
with  them,  is  a  different  fluid,  having  a  different  compo- 
sition, which  will  be  described  in  discussing  the  coagu- 
lation of  blood. 

Composition  of  Plasma. — Blood-plasma  contains  the 
following  constituents :  water,  fibrinogen,  paraglobulin, 
serum-albumin,  fat,  soaps,  cholesterin,  lecithin,  glucose, 
urea,  uric  acid,  creatin,  lutein,  sodium  chloride,  sodium 
carbonate,  calcium  phosphate,  and  some  others  which 
need  not  be  specified.  Blood-plasma  also  contains  the 
following  gases  :  carbon  dioxide,  nitrogen,  and  oxygen. 

Coagulation  of  Blood. — When  blood  is  withdrawn  from 
the  circulation  it  undergoes  coagulation,  consisting  in 
the  production  of  a  clot  from  which  is  subsequently  ex- 
pressed a  fluid  called  the  "  serum."  The  length  of  time 
required  for  coagulation  varies  in  different  animals.  In 
human  blood  the  change  manifests  itself  in  about  two  or 
three  minutes.  When  the  blood  is  withdrawn  from  the 
vessel  it  is  fluid,  but  at  the  end  of  two  or  three  minutes 
its  fluidity  is  so  much  diminished  that  it  will  not  flow ; 
this  consistency  increases  until  at  the  end  of  eight  or  ten 
minutes  the  entire  quantity  of  blood  becomes  a  mass 
resembling  currant  jelly  in  color  and  consistency.  This 
jelly-like   mass   becomes    more   and    more   consistent, 


144  HUMAN  PHYSIOLOGY. 

squeezing  out  upon  its  surface  a  few  drops  of  a  straw- 
colored  fluid — the  serum.  As  the  shrinking  of  this 
gelatinous  mass — the  clot — continues,  it  separates  from 
the  sides  of  the  vessel  in  which  the  blood  was  received, 
and  the  serum  is  squeezed  out  on  all  sides,  until  at 
length  there  is  a  more  or  less  solid  clot  floating  in  a 
considerable  quantity  of  serum.  When  examined  the 
clot  is  found  to  be  made  up  of  fibrin  and  corpuscles,  the 
red  corpuscles  giving  to  it  the  red  color.  The  serum 
has  the  same  composition  as  the  plasma,  minus  the 
fibrinogen. 

Although  the  corpuscles  are  denser  than  the  plasma, 
still  the  difference  is  so  slight  and  the  process  of 
coagulation  so  rapid  that  before  they  can  settle  they 
are  entangled  in  the  meshes  of  the  fibrin  as  it  forms, 
and  thus  become  a  part  of  the  clot.  If  anything  occur 
to  delay  coagulation,  the  corpuscles  settle,  and  the  clot 
is  then  less  red  and  more  yellowish.  This  delay  may 
be  brought  about  by  the  addition  of  a  solution  of  mag- 
nesium sulphate ;  it  occurs  also  in  inflammatory  pro- 
cesses, and  hence  in  the  olden  time,  when  venesection 
was  commonly  practised,  this  crusta  pJilogistica,  or  "bufly 
coat,"  was  always  looked  for  by  the  physician,  and  when 
it  formed  was  considered  as  evidence  that  the  bleeding 
was  justifiable.  That  the  physicians  of  that  period  were 
not  always  right  in  this  judgment  is  now  known,  for  a 
buffy  coat  will  form  in  blood  which  is  hydraemic,  a  con- 
dition in  which  bleeding  is  contraindicated.  In  horses' 
blood,  which  normally  coagulates  very  slowly,  this 
"  buffy  coat "  always  forms.  It  is  simply  the  fibrin 
without  the  corpuscles,  or  at  least  without  enough  of 
them  to  give  the  red  color  which  the  clot  usually 
possesses. 


ABSORPTION.  145 

Influences  zvhich  Retard  Coagulation. — Coagulation  is 
retarded  by  cold,  by  solutions  of  sodium  or  magnesium 
sulphate,  by  a  diminished  amount  of  oxygen,  by  an  in- 
creased amount  of  carbon  dioxide,  by  acids  or  alkalies, 
by  egg-albumin,  by  oil,  by  a  solution  of  albumose,  and 
by  an  infusion  of  the  leech,  which  doubtless  contains 
an  albumose.  Venous  blood  coagulates  more  slowly 
than  arterial,  because  of  the  lessened  amount  of  oxygen 
and  the  increased  amount  of  carbon  dioxide.  It  is  said 
that  blood  from  the  capillaries  does  not  coagulate  at  all. 

It  is  the  prevalent  opinion  that  menstrual  blood  does 
not  clot ;  this,  strictly  speaking,  is  not  true.  If  the  blood 
as  it  comes  from  the  uterine  vessels  were  collected,  it 
would  doubtless  coagulate  as  does  other  blood,  but 
when  it  is  mixed  with  the  acid  vaginal  mucus  its  coag- 
ulation is  then  impeded.  Then,  too,  during  the  men- 
strual period  some  of  the  blood  undergoes  clotting 
within  the  uterine  cavity  or  in  the  vagina:  that  which 
escapes  and  which  is  regarded  as  menstrual  blood  is 
for  the  most  part  only  serum,  which  of  course  does  not 
coagulate. 

Influences  that  Hasten  Coagulation. — Coagulation  is 
promoted  by  warmth  and  by  contact  with  roughened 
surfaces. 

Causes  of  Coagulation. — Perhaps  no  physiological 
question  has  excited  more  controversy  than  that  which 
deals  with  the  cause  of  blood-coagulation.  Normally, 
blood  remains  fluid  within  the  blood-vessels,  but  within 
three  minutes  after  withdrawal  it  begins  to  undergo  co- 
agulation.    What  is  the  explanation  ? 

It  has  been  suggested  that  blood-coagulation  is  due 
to  exposure  to  the  air.  It  is  true  that  contact  with  the 
air  hastens  coagulation,  but  that  this  is  unnecessary  to 
10 


146  HUMAN  PHYSIOLOGY. 

the  process  is  shown  by  the  fact  that  coagulation  will 
take  place  under  mercury,  when  all  air  is  excluded. 
Nor  can  it  be  due  to  the  cooling  the  blood  undergoes 
when  it  is  exposed  to  the  air,  for,  as  already  noted,  cold 
retards  coagulation,  while  heat  aids  it.  It  has  also  been 
suggested  that  the  fluid  condition  of  the  blood  in  the 
circulation  is  due  to  its  motion,  and  that  it  clots  when 
it  comes  to  a  state  of  rest.  But  experiment  shows  that 
motion,  such  as  the  beating  of  blood  with  agitation, 
hastens  coagulation. 

Experiments  demonstrate  that  the  fluidity  of  the  blood 
is  maintained  only  when  the  blood  is  in  contact  with  the 
normal  lining  membrane  of  the  blood-vessels :  when 
this  relation  is  interrupted,  either  by  disease,  or  by  death 
or  injury  of  the  membrane,  or  by  withdrawal  of  the 
blood  from  the  vessel,  this  fluidity  ceases  and  the  blood 
coagulates. 

The  clot  that  forms  in  the  coagulation  is  fibrin,  in  the 
meshes  of  which  the  corpuscles  become  entangled.  This 
fibrin  is  the  coagulated  fibrinogen  of  the  blood,  and  the 
factor  which  causes  it  to  coagulate  is  fibrin-ferment. 
The  preponderance  of  evidence  at  the  present  time  points 
to  the  white  corpuscles  as  the  source  of  this  ferment, 
although  this  has  not  been  definitely  proved  to  be  its 
origin. 

The  presence  of  lime-salts  in  the  blood  is  very  import- 
ant in  the  process  of  coagulation,  although  it  cannot 
perhaps  be  said  that  they  are  absolutely  essential,  as  is 
the  case  with  casein,  which  is  not  coagulated  by  rennin 
unless  these  salts  be  present. 

The  property  of  coagulation  possessed  by  blood  is  of 
great  service  in  arresting  hemorrhage.  There  are  indi- 
viduals in  whom  bleeding,  which  to  most  people  would 


ABSORPTION.  147 

be  only  slight,  amounts  to  a  dangerous  haemorrhage, 
often  requiring  surgical  skill  for  its  arrest,  and  in  some 
instances  being  so  uncontrollable,  even  by  the  most  skil- 
ful treatment,  that  death  results.  Such  persons  are 
called  "  bleeders,"  and  on  them  surgeons  hesitate  to 
perform  any  operation,  however  trivial,  the  extraction  of  a 
tooth  even  being  often  followed  by  an  alarming  loss  of 
blood.  This  condition  is  spoken  of  as  "  haemophilia  " 
or  "  haemorrhagic  diathesis."  It  is  probable  that  in  such 
cases  the  fibrinogen  is  very  deficient. 

Blood,  then,  before  coagulation  consists  of  plasma  and 
corpuscles ;  after  coagulation,  of  serum  and  clot,  the 
serum  having  the  same  composition  as  the  plasma,  save 
that  it  has  lost  the  fibrinogen,  which,  having  assumed  a 
new  form,  fibrin,  exists  in  the  clot  together  with  the 
corpuscles. 

Gases  in  the  Blood. — The  blood  contains  nitrogen, 
oxygen,  and  carbon  dioxide.  The  first  of  these  gases 
exists  in  the  proportion  of  from  i  to  2  per  cent.,  and  is 
practically  the  same  in  both  arterial  and  venous  blood. 
Nitrogen  has  no  special  physiological  interest.  The 
amount  of  carbon  dioxide  and  of  oxygen  varies  greatly 
in  different  portions  of  the  circulatory  apparatus  and 
under  different  circumstances.  The  variations,  indeed, 
are  so  great  that  it  is  possible  to  give  only  general 
averages.  The  amount  in  human  arterial  blood  has 
been  given  as  21.6  volumes  per  cent.;  that  is,  in  every 
100  volumes  of  arterial  blood  there  are  21.6  volumes  of 
oxygen.  In  venous  blood  the  percentage  is  but  6.8. 
Another  estimate  gives  the  oxygen  in  arterial  blood  as 
20  per  cent,  and  in  venous  blood  as  from  8  to  12  per 
cent.  The  blood  in  these  estimates  is  presumed  to  be 
at  0°  C.  and  the  pressure  to   be  760  mm.  of  mercury. 


148  HUMAN  PHYSIOLOGY. 

The  following  figures  illustrate  the  difference  in  the 
amount  of  this  gas  in  the  different  vessels  and  in  the 
same  vessel  under  different  circumstances :  Oxygen  in 
carotid  artery,  21  per  cent.;  in  renal  artery,  19;  in  renal 
vein  (kidney  active),  17;  in  renal  vein  (kidney  at  rest), 
6.  In  the  blood  of  asphyxiated  animals  oxygen  may 
entirely  be  absent. 

The  difference  between  the  amount  of  oxygen  in  the 
renal  vein  when  the  kidney  is  active  and  when  it  is  at 
rest  (and  what  is  true  of  the  kidney  is  true  of  other 
glands)  needs  some  explanation.  When  the  kidney  is 
at  rest  only  enough  blood  goes  to  it  to  nourish  it  and  to 
supply  the  small  amount  of  oxygen  which  it  needs  in  a 
resting  state ;  the  blood  that  returns  from  it  is  venous 
blood,  in  which  the  amount  of  oxygen  is  but  6  per  cent. 
When,  however,  the  gland  is  actively  at  work,  the 
amount  of  blood  which  goes  to  the  kidney  is  greatly  in 
excess  of  the  amount  needed  for  nutritive  purposes,  the 
surplus  being  for  the  specific  purposes  of  the  gland ; 
and,  although  more  oxygen  is  taken  from  it  than  when 
the  gland  is  quiescent,  still  the  proportion  thus  taken, 
compared  with  the  amount  of  blood  which  traverses  the 
gland,  is  so  small  that  when  it  leaves  the  gland  it  con- 
tains nearly  as  great  a  percentage  of  oxygen  as  before. 
Thus,  the  oxygen  in  the  renal  artery  under  these  cir- 
cumstances is  19  per  cent.,  and  in  the  renal  vein  17  per 
cent. 

It  has  already  been  stated  that  this  oxygen  is  combined 
with  the  haemoglobin  in  the  red  corpuscles,  the  amount 
in  the  plasma  being  0.26  per  cent. — no  more  than  would 
be  found  in  an  equal  amount  of  distilled  water. 

Carbon  dioxide  exists  in  human  arterial  blood  to  the 
amount  of  about  40  per  cent.,  and  in  venous  blood  about 


RESPIRA  TION.  1 49 

48  per  cent.  This  may  be  greatly  increased  in  asphyxia, 
when  it  has  been  found  to  be  69.21  per  cent.  One-third 
of  the  carbon  dioxide  is  in  the  corpuscles,  a  small  part 
of  this  being  in  the  leucocytes,  the  remaining  two-thirds 
being  in  the  plasma,  some  simply  absorbed  (perhaps  one- 
tenth),  and  some  combined  to  form  sodium  carbonate  and 
bicarbonate. 

3.  Respiration. 

One  of  the  most  important  processes  carried  on  in 
the  body  is  that  by  which  the  tissues  receive  oxygen. 
In  animals  whose  structure  is  exceeding  simple,  and 
so  constituted  that  all  portions  of  their  bodies  are 
bathed  by  the  oxygen-carrying  medium,  the  oxygen 
is  directly  absorbed,  but  in  those  in  which  there  are 
tissues  remotely  situated  as  regards  this  medium,  some 
provision  must  be  made  for  conveying  the  oxygen 
from  the  medium  to  the  tissues.  This  condition  exists 
in  man,  many  of  whose  tissues  are  so  deeply  situated 
that  without  such  provision  the  maintenance  of  life 
would  be  impossible.  In  man  this  medium  is  the  blood. 
But  additional  provision  must  be  made  for  the  renewal 
of  the  oxygen  abstracted  by  the  tissues.  That  part  of 
the  process  by  which  the  tissues  take  oxygen  from  the 
blood  is  internal  respiration,  and  that  part  by  which  the 
renewal  is  accomplished  is  external  respiration.  Ordi- 
narily, when  respiration  is  spoken  of  without  qualifica- 
tion it  is  external   respiration  that  is  referred  to. 

Respiratory  Apparatus. — The  group  of  organs  con- 
cerned in  external  respiration  is  collectively  spoken  of 
as  the  "  respiratory  apparatus,"  which  consists  of  the 
nose,  larynx,  trachea,  bronchial  tubes,  lungs,  and  thorax. 

The  nose  is  the  beginning  of  the  air-passages,  for, 


I50  HUMAN  PHYSIOLOGY. 

although  it  is  regarded  by  many  as  the  organ  of  smell 
only,  it  has  another  function  as  well.  The  mouth  be- 
longs to  the  alimentary  canal,  and  should  only  be  opened 
to  take  in  food  or  to  speak,  never  to  take  in  air.  The 
proper  channel  for  the  admission  of  air  is  the  nose,  and 
the  use  of  the  mouth  for  this  purpose  is  not  physiolog- 
ical. Indeed,  man  is  said  to  be  the  only  animal  that 
breathes  through  the  mouth.  If  the  nursing  child  should 
attempt  to  use  its  mouth  for  the  admission  of  air  to  the 
lungs,  sucking  could  not  be  performed  without  great 
difficulty,  and  after  a  few  moments  the  child  would  be 
compelled  to  let  go  the  breast  in  order  not  to  suffocate. 

Mouth-breathing . — There  is  no  more  pernicious  habit, 
so  far  as  health  is  concerned,  than  breathing  through  the 
mouth.  If  this  be  due  simply  to  habit  and  nothing  else, 
it  may  be  overcome,  but  if,  as  is  often  the  case,  it  be  due 
to  some  diseased  condition  of  the  nose,  or  to  the  presence 
in  the  nasal  cavities  of  tumors,  or  to  the  existence  of 
enlarged  tonsils,  its  relief  can  only  be  accomplished  by 
surgical  means.  The  function  of  the  nose  in  respiration 
is  to  warm  the  air  and  to  filter  out  from  it  dust  and  other 
extraneous  matter  which  would  otherwise  enter  the  air- 
passages  and  cause  irritation.  When  air  is  taken  in  by 
the  mouth  these  advantages  are  lost. 

Mouth-breathing  causes  dryness  of  the  mouth  and  the 
pharynx,  which  dryness  is  very  noticeable  on  awaking 
from  sleep.  The  mucous  membrane  becomes  congested 
and  inflammation  is  likely  to  follow.  A  chronic  inflam- 
matory condition  of  the  larynx  may  also  result  from 
this  cause,  and  the  evidence  is  very  conclusive  that  the 
hearing  becomes  affected  in  these  cases.  The  deformity 
'kx\.o^Vi2i?,  pigeon-breast  is  not  an  uncommon  sequel.  In- 
deed, the  consequences  of  mouth-breathing  are  numer- 


R  ESP  IRA  TION. 


151 


ous,  widespread,  and  serious,  and  the  subject  has  never 
received  the  attention  which  its  importance  demands. 

The  anatomical  structures  in  the  larynx  having  spe- 
cial physiological  interest  in  connection  with  the  pro- 
cess of  respiration  are  the  arytenoid  cartilages,  the  vocal 
cords,  and  the  posterior  crico-arytenoid  muscles.     The 


Fig.  21. — t,  larynx:  2,  crico-thyroid  muscles;  3,  trachea;  4-6,  right  lung;  7,8,  left 
lung;  9,  pericardium;  10,  mediastinum;  ii  and  14,  subclavian  arteries;  12,  13, 
carotid  arteries  ;  15,  16,  innominate  veins  ;  17,  20,  subclavian  veins;  18,  19,  internal 
ji'gular  veins  ;  21,  root  of  lung.  ■  The  lungs  naturally  cover  the  pericardium,  but  ii* 
the  figure  are  represented  as  held  back  by  hooks. 

space  between  the  vocal  cords  is  the  rbna  glottidis,  or 
glottis. 

The  trachea,  or  windpipe,  is  a  tube  about  1 1.5  cm.  inches 
in  length,  and  it  extends  from  the  larynx  to  the  bronchi. 


152 


HUMAN  PHYSIOL  OG  Y. 


into  which  it  divides  (Fig.  21).  It  is  made  up  of  rings 
of  cartilage  which  are  incomplete  behind,  their  ends  be- 
ing joined  by  fibrous  membrane ;  here  the  trachea  is  in 
contact  with  the  oesophagus.  The  cartilages  are  joined 
to  one  another  by  similar  membrane.  The  trachea  is 
lined  with  mucous  membrane,  the  epithelium  of  which 
is  of  the  columnar  ciliated  variety. 

The  bronchi  are  two  in  number,  the  right  bronchus 
going  to  the  right  lung,  and  the  left  bronchus  to  the 
left  lung. 

The  lungs,  two  in  number,  are  covered  by  the  visceral 
layer  of  the  pleura.  Each  bronchus  as  it  enters  the 
lungs  divides,  the  branches  which  result  from  this  divis- 
ion again  divide,  and  so  on,  until  the  last  subdivision  is 


Fig.  22. — a,  vertebral  column  ;  b,  clavicle  ;  d,  ribs  ;  e,  sternum. 

reached,  the  ultimate  or  lobular  bronchial  tube,  which 
passes  into  a  lobule  which  is  made  up  of  air-cells.     The 


KESPIRA  TION. 


153 


walls  of  the  air-cells  are  composed  of  elastic  tissue,  and  in 
them  are  the  capillary  blood-vessels. 

TJie  thorax,  the  cavity  in  which  the  lungs  are  situated, 
is  composed  of  the  vertebral  column,  the  ribs,  the  sternum, 
the  diaphragm,  and  the  muscles  (intercostals)  between 
the  ribs  and  those  which  cover  them  (Fig.  22).  The 
vertebral  column  is  rigid,  and  takes  no  part  in  an)-  of 
the  movements  connected  with  respiration,  but  with  a 
portion  of  it  the  heads  of  the  ribs  articulate.  The  ribs 
are  connected  posteriorly  with  the  vertebral  column,  as 
stated,  and  anteriorly  with  the  sternum  by  means  of  the 
costal  cartilages.  The  general  direction  of  the  ribs  is 
such  that  their  vertebral  extremities  are  higher  than  the 
sternal.    The  diaphragm  (Fig.  23)  is  the  lower  boundary 


Fig.  23— Interior  View  of  the  Diaphragm :  1-3,  the  three  lobes  of  the  central  tendon 
surrounded  by  the  fleshy  fasciculi  derived  from  the  inferior  margin  of  the  thorax  ;  4,  5, 
the  crura  ;  6,  7,  the  arcuate  ligaments  ;  8,  aortic  orifice  ;  9,  oesophageal  orifice;  10, 
quadrate  foramen  :  11,  psoas  muscle  ;   12,  quadrate  lumbar  muscle. 

of  the  thoracic  cavity,  separating  it  from  that  of  the  ab- 
domen.    The  central  portion  is  tendinous  in  structure, 


154  HUMAN  PHYSIOLOGY. 

while  the  peripheral  portion  is  muscular.  It  is  attached 
to  the  interior  of  the  thorax/and  forms  an  arch  with  its 
convexity  directed  upward,  the  summit  of  the  arch  being 
at  the  level  of  the  fifth  rib.  The  intercostal  muscles,  as 
their  name  implies,  are  between  the  ribs.  The  fibres  of 
the  external  intercostal  muscles  are  directed  downward 
and  forward,  while  the  direction  of  those  of  the  internal 
is  upward  and  forward. 

Respiratory  Movements. — The  respiratory  movements 
are  of  two  kinds — inspiratory  and  expiratory. 

Inspiratory  Movements. — By  virtue  of  the  inspiratory 
movements  the  air  passes  into  the  lungs.  During  their 
performance  the  thorax  expands  under  the  influence  of 
the  diaphragm  and  the  external  intercostal  muscles.  In 
inspiration  all  the  diameters  of  the  chest  are  increased. 
The  descent  of  the  diaphragm  increases  the  vertical 
diameter  (PI.  i).  This  is  accomplished  by  the  contrac- 
tion of  the  muscular  portion,  and  as  the  fibres  shorten 
the  tendinous  portion  is  drawn  downward,  diminishing 
very  considerably  the  convexity  of  the  arch.  In  this 
descent  the  organs  of  the  abdominal  cavity  are  pressed 
down  and  are  also  compressed.  This  displacement 
causes  a  protrusion  of  the  abdominal  walls.  At  the 
same  time  that  these  changes  are  going  on,  increasing 
the  vertical  diameter  of  the  thorax,  the  transverse  and 
antero-posterior  diameters  are  also  being  increased.  The 
scaleni  muscles  are  attached  to  the  cervical  vertebrae  and 
the  first  and  second  ribs.  By  their  contraction  these 
ribs  are  firmly  fixed,  and  then,  the  external  intercostals 
contracting,  the  ribs  are  raised,  rotating  at  their  articula- 
tion with  the  vertebrae.  The  shape  and  direction  of  the 
ribs  are  such  that  when  they  are  raised  their  convexities 
are  carried  outward,  and   thus  the  transverse  diameter 


RESPIRA  TION.  1 5  5 

of  the  thorax  is  increased.  But  this  movement  also  car- 
ries the  sternum  forward,  thereby  increasing  the  antero- 
posterior diameter.  Under  some  circumstances,  as  when 
there  is  some  obstruction  to  the  entrance  of  air,  addi- 
tional muscles,  called  "extraordinary  muscles  of  inspira- 
tion," are  brought  into  action.  In  this  way  mo.st  of  the 
muscles  about  the  thorax  may  be  called  upon.  This  is 
known  as  "  forced  inspiration."  It  should  be  noted  that 
inspiration  is  an  active  process  ;  that  is,  one  that  requires 
for  its  performance  the  action  of  muscles. 

Expiratory  Movements  are  for  the  most  part  passive 
in  their  nature ;  that  is,  are  not  due  to  muscular  con- 
traction. During  the  descent  of  the  diaphragm,  referred 
to  in  describing  the  inspiratory  movements,  the  elastic 
abdominal  organs  and  their  attachments  and  the  abdom- 
inal walls  are  put  upon  the  stretch.  At  the  end  of  the 
inspiratory  act  the  diaphragm  ceases  to  contract,  and  by 
virtue  of  the  elasticity  of  these  structures  the  contents  of 
the  abdomen  return  to  the  position  they  occupied  at  the 
beginning  of  the  diaphragm's  descent,  and  in  so  doing 
this  structure  is  carried  back  to  its  original  position.  The 
elevation  of  the  ribs  by  the  contraction  of  the  external 
intercostals  during  inspiration  twists  the  elastic  costal 
cartilages  which  join  the  ribs  to  the  sternum  :  as  soon 
as  these  muscles  cease  to  contract  these  cartilages  un- 
twist, and  in  so  doing  aid  in  the  return  of  the  ribs.  In 
describing  the  structure  of  the  lungs  it  was  stated  that 
the  walls  of  the  lobules  were  rich  in  elastic  tissue  :  in 
inspiration  these  lobules  are  greatly  distended,  their 
walls  being  put  on  the  stretch.  When  the  inspiratory 
forces  cease  to  act,  then  this  tissue,  by  virtue  of  its  elas- 
ticity, returns  to  its  former  condition,  and  in  so  doing 
expels  the  air,  constituting  expiration.    Contractility  may 


156 


HUMAN  PHYSIOLOGY. 


be  said  to  be  the  inspiratory  force ;  elasticity,  the  ex- 
piratory force. 

As  in  inspiration,  so  in  expiration,  there  are  occasions 
when  obstruction  to  the  outgoing  air  exists,  and  forced 
expiration  becomes  necessary.  The  muscles  concerned 
in  this  act  are  the  internal  intercostals,  and  others  known 
as  "  extraordinary  muscles  of  expiration,"  whose  ar- 
rangement is  such  that  in  their  contraction  the  capa- 
city of  the  thorax  is  diminished.  The  abdominal  walls, 
by  exerting  pressure  on  the  abdominal  viscera,  and  thus 
on  the  diaphragm,  still  further  diminish  the  thoracic 
cavity  and  force  out  the  contained  air. 

Movements  of  Glottis. — There  are  in  connection  with 
the  process  of  respiration  certain  movements  of  the  glot- 
tis which  are  important.  On  examination  of  the  interior 
of  the  larynx  it  will  be  seen  that  during  inspiration  the 
vocal  cords  separate,  and  during  expiration  approach 
each  other.  During  deep  breathing  (Fig.  25)  the  sep- 
aration of  the  cords  is  greater  than  in  quiet  breathing 
(Fig.  24). 


Fig.  24. — The  Larynx  in  Gentle  Breath- 
ing (Lennox-Browne):  L,  epiglottis; 
V,  vocal  cords ;  S,  cartilages  of  San- 
torini,  which  surmount  the  arytenoid 
cartilages;    P,  P,  ventricular  bands. 


Fig.  25  — The  Larynx  in  Deep  Breathing 
(Lennox-Browne)  :  W,P,  tracheal  rings  ; 
B,  openings  of  bronchi ;  P,  P,  ventric- 
ular bands. 


The  area  of  the  trachea  is  nearly  three  times  that  of 
the  space  between  the  cords  at  the  beginning  of  inspira- 
tion. The  separation  of  these  cords  is  effected  by  the 
contraction    of  the    po.sterior    crico-arytenoid    muscles, 


R  ESP  IRA  TION.  1 5  7 

which  by  their  attachment  to  the  arytenoid  carti- 
lages rotate  these  outward,  and  thus  separate  the  pos- 
terior ends  of  the  cords  which  are  attached  to  them, 
increasing  the  area  nearly  twofold.  When  these  muscles 
cease  their  contraction,  as  they  do  at  the  end  of  the  in- 
spiratory act,  then  the  elasticity  of  the  cartilages  brings 
the  muscles  back  to  the  position  they  occupied  at  the 
beginning  of  inspiration.  These  movements  of  the 
glottis  occur  synchronously  with  the  respiratory  move- 
ments of  the  thorax. 

Capacity  of  tJie  Lungs. — At  the  beginning  of  an  ordi- 
nary inspiration  the  lungs  contain  3280  cc.  of  air,  which 
so  distends  the  lungs  that  the  visceral  layer  of  the  pleura 
is  in  contact  with  the  parietal  layer.  As  the  thorax  en- 
larges the  air  in  the  lungs  distends  them  still  more,  so 
that  they  are  still  kept  in  contact  with  the  thoracic  walls. 
This  contact  between  the  visceral  and  parietal  layers  of 
the  pleura  is  constant,  irrespective  of  the  amount  of  dis- 
tention of  the  lungs.  The  expansion  of  the  air  in  the 
lungs  makes  it  of  less  density  than  the  external  air  with 
which  it  is  in  communication  through  the  air-passages, 
and  immediately  there  is  a  flow  of  external  air  into  these 
passages  to  establish  an  equilibrium  :  this  inflow  con- 
stitutes inspiration.  The  amount  of  air  which  thus  flows 
in  is  ordinarily  500  cc.  During  expiration  this  amount 
is  forced  out  by  the  mechanism  already  described.  To 
the  air  which  flows  in  and  out  during  ordinary  respiration 
the  name  of  "  tidal  air  "  is  given,  from  the  resemblance 
which  the  process  bears  to  the  ebb  and  flow  of  the  tide. 
At  the  end  of  an  ordinary  expiration  there  remain  in  the 
lungs,  as  already  stated,  upward  of  3000  cc.  of  air.  By  a 
forced  expiration  1640  cc.  of  air  may  be  expelled  ;  this  is 
the  reserve  or  supplemental  air.    When  this  expulsion  has 


158  HUMAN  PHYSIOLOGY. 

been  accomplished  there  still  remains  1640  cc.  of"  resid- 
ual" air,  which  cannot  be  expelled,  no  matter  how  great 
the  effort.  Since  this  residual  and  supplemental  air  or- 
dinarily remains  in  the  lungs  during  respiration,  it  is 
spoken  of  as  the  "  stationary  air."  After  breathing  in 
the  tidal  air  there  may,  however,  be  taken  in,  by  forced 
inspiration,  about  1600  cc.  of  air;  this  is  the  "  comple- 
mental  air." 

Vital  Capacity. — The  volume  of  air  over  which  an 
individual  can  exert  control  is  known  as  his  "  vital 
capacity."  It  is  the  sum  of  the  complemental,  tidal,  and 
supplemental  air,  and  excludes  the  residual. 

Frequency  of  Respiration. — In  the  new-born  child  the 
number  of  respirations  per  minute  is  44;  at  five  years 
of  age,  26;  at  twenty  years,  20;  and  at  thirty  years,  16. 
These  figures  represent  an  average  during  a  quiescent 
condition.  Should  the  respirations  be  counted  during 
sleep,  they  would  be  one  or  two  less  per  minute  ;  during 
great  activity  they  would  be  increased  considerably,  in 
the  adult  running  up  to  30  or  more. 

Cause  of  Respiration. — The  discussion  of  the  cause  of 
respiratory  movements  will  be  deferred  until  the  function 
of  the  respiratory  centre  of  the  medulla  oblongata  is 
considered. 

Types  of  Respiration. — It  has  been  the  practice  among 
physiological  writers  to  speak  of  the  "  costal,"  or  female, 
type  of  respiration,  and  the  "  abdominal,"  or  male,  type. 
The  following  condensed  statement  from  one  of  the  best 
text-books  on  this  subject  represents  the  views  of  these 
writers :  "  In  children,  as  well  as  in  the  adult  male, 
under  ordinary  conditions,  the  diaphragm  performs 
most  of  the  work,  and  the  movements  of  the  abdomen 
are   the    only    ones    especially   noticeable.  ...  In   the 


.   RESPIRATION.  I  59 

female  the  movements  of  the  chest,  particularly  of  its 
upper  half,  are  habitually  more  prominent  than  those  of 
the  abdomen,  and  this  difference  in  the  mechanism  of 
respiration  is  characteristic  of  the  sexes."  The  costal 
type  of  respiration  here  spoken  of  as  characteristic  of 
the  female  was  supposed  to  be  a  wise  provision  of  nature, 
in  order  that  when  pregnancy  should  occur  the  respira- 
tory movements  would  not  be  interfered  with,  as  they 
would  be  had  the  female  possessed  the  abdominal  type 
of  respiration  seen  in  the  male. 

Very  careful  and  complete  studies  of  women  in  and 
out  of  civilization,  the  lower  portions  of  whose  chests 
have  never  been  compressed  with  corsets  or  with  other 
devices  calculated  to  prevent  expansion  of  those  parts, 
have  demonstrated  that  the  supposed  respiratory  differ- 
ence in  male  and  female  does  not  exist  naturally,  and 
that  when  it  is  found  it  is  due  to  the  corset  and  not  to 
any  peculiarity  of  sex.  Indeed,  if  the  male  chest  be  en- 
cased in  the  corset  the  abdominal  type  becomes  changed 
at  once  into  the  costal.  It  is  also  of  interest  to  note  that 
in  one  case  at  least  where  the  observation  was  made- 
abdominal  respiration  was  well  marked  in  a  pregnant 
woman  within  one  week  of  her  confinement. 

Chemistry  of  Respiration. — The  air  contains  20.96 
parts  by  volume  of  oxygen,  79.02  parts  of  nitrogen,  and 
0.03  parts  of  carbon  dioxide.  Watery  vapor  is  also 
present,  the  amount  varying  under  different  circum- 
stances, being  greater  the  higher  the  temperature  of  the 
air.  The  term  absolute  humidity  has  reference  to  the 
total  amount  of  watery  vapor  which  a  volume  of  air 
contains,  irrespective  of  the  question  of  temperature ;  the 
term  relative  humidity  is  used  to  express  the  proportion 
of  watery  vapor  present  in  the  air  at  certain  temperatures 


l6o  HUMAN  PHYSIOLOGY. 

as  compared  with  air  fully  saturated,  saturation  being 
expressed  by  lOO.  Absolute  humidity  is  expressed  in 
grammes  per  cubic  metre  or  in  grains  per  cubic  foot, 
while  relative  humidity  is  expressed  in  percentages. 
Thus  if  the  temperature  of  the  air  be  4°,  and  it  is 
saturated  with  watery  vapor,  its  relative  humidity  would 
be  said  to  be  lOO;  if,  now,  its  temperature  were  raised 
to  27°,  its  relative  humidity  would  be  only  24,  because 
the  higher  the  temperature  the  more  vapor  can  a  given 
volume  of  air  contain,  and  the  air  at  27°  would  hold  a 
much  greater  amount  than  when  its  temperature  was  4°. 

The  amount  of  moisture  present  in  air  is  an  important 
factor  in  the  preservation  of  health.  If  it  be  too  dry,  the 
air-passages  are  irritated,  while  if  too  moist  there  is  pro- 
duced a  feeling  of  oppression.  A  relative  humidity  of 
70  is,  as  a  rule,  very  agreeable.  Traces  of  ammonia  are 
also  found  in  the  atmospheric  air.  Besides  these  con- 
stituents, which  are  universal,  there  are  many  others 
that  may  or  may  not  be  present  as  the  result  of  pro- 
cesses of  manufacture. 

Expired  Air. — When  the  atmospheric  air  has  been 
breathed  its  composition  is  markedly  changed  in  the 
following  particulars:  i.  It  has  gained  carbon  dioxide, 
the  amount  being  increased  from  0.03  parts  per  cent,  to 
4.38.  2.  It  has  lost  oxygen,  the  20.96  volumes  per  cent, 
being  reduced  to  16.03,  o^"  about  5  per  cent.  It  should 
be  noted  that  the  loss  of  oxygen  is  greater  than  can  be 
accounted  for  by  the  amount  of  that  gas  returned  in  the 
carbon  dioxide,  the  difference  representing  the  amount 
used  up  in  processes  of  oxidation  constantly  going  on  in 
the  body.  3.  It  has  gained  watery  vapor,  the  expired 
air  being  saturated.  The  actual  amount  of  vapor  which 
it  receives  while  in  the  lungs  will  of  course  vary.    If  the 


R  ESP  IRA  TION.  1 6 1 

air  when  inspired  be  cool  and  dry,  it  will  take  more 
moisture  from  the  body  than  if  it  be  moist  and  warm. 
The  daily  loss  to  the  body  through  this  channel  is  255 
grammes.  4.  The  expired  air  is,  as  a  rule,  warmer  than 
the  inspired,  under  ordinary  circumstances  being  36°  C. 
Thus,  if  the  temperature  of  the  air  be  21°  C,  it  will  gain 
15°  C.  while  in  the  lungs.  The  temperature  of  the  ex- 
pired air  is  very  nearly  36°,  whatever  that  of  the  atmo- 
spheric air  may  be.  5.  The  expired  air  contains  certain 
volatile  organic  matters  which  are  at  once  recognized  by 
the  sense  of  smell,  although  the  chemist  has  not  yet  made 
us  acquainted  with  their  exact  composition.  These  or- 
ganic constituents  are  of  great  importance,  and  will  be 
discussed  later. 

Ventilation. — It  is  manifest  that  if  at  each  inspira- 
tion oxygen  be  abstracted  from  the  air,  in  the  course 
of  time  the  amount  of  this  gas  will  be  so  reduced  as  to 
make  its  want  seriously  felt.  It  is  necessary,  therefore, 
in  order  to  keep  the  amount  of  oxygen  up  to  the  stand- 
ard, that  some  provision  should  be  made  to  supply  it. 
Besides  the  removal  of  the  oxygen,  the  air  is  still  further 
rendered  unsuited  for  respiratory  purposes  by  the  carbon 
dioxide,  and  especially  by  the  organic  matter  thrown  off 
by  the  expired  air ;  the  oxygen  being  still  further  dimin- 
ished by  stoves  and  lights,  and  the  air  being  vitiated  by 
the  products  of  combustion.  To  supply  oxygen  and 
to  remove  these  impurities  is  the  object  of  ventilation. 

A  common  test  to  determine  whether  the  air  of  an 
apartment  contains  sufficient  oxygen  for  respiratory  pur- 
poses is  to  see  if  a  candle  will  burn  in  it.  This  test  is 
used  to  determine  whether  the  air  in  vaults  or  in  exca- 
vations is  fit  for  respiration.  A  candle  will  not  burn  if 
the  air  contain  only  17  per  cent,  of  oxygen.  A  man 
11 


1 62  HUMAN  PHYSIOLOGY. 

could  breathe,  however,  if  this  amount  were  present,  but 
if  it  were  reduced  to  lo  per  cent.,  asphyxia  would  be 
produced.  So  far,  then,  as  the  question  of  oxygen  is 
concerned,  a  man  could  breathe  where  a  candle  would 
not  burn,  but  it  does  not  necessarily  follow  that  it  is 
always  safe  for  a  man  to  venture  where  a  candle  will 
burn,  for  sometimes,  although  there  may  be  oxygen  suf- 
ficient to  sustain  life,  poisonous  gases  may  also  be  present 
in  an  amount  sufficient  to  produce  a  fatal  result.  It  would 
be  a  surer  test  to  place  a  dog  in  the  suspected  place  and 
leave  him  there  for  twenty  minutes.  If  he  survive,  it 
will  be  safe  for  a  man  to  enter. 

It  is  a  general  impression  that  the  carbon  dioxide 
which  accumulates  in  a  room  where  a  large  number 
of  persons  is  congregated  is  the  ingredient  of  the  air 
which  makes  its  use  in  respiration  so  injurious;  but  this 
is  not  the  fact.  An  atmosphere  containing  as  much  as 
2  per  cent,  of  carbon  dioxide,  as  in  factories  where  so- 
called  "soda-water"  is  made,  may  be  breathed  without 
injury  or  even  inconvenience,  while  one  in  which  this  gas 
exceeds  0.07  per  cent.,  provided  it  have  its  origin  in  the 
lungs,  is  regarded  by  sanitarians  as  containing  the  max- 
imum amount  that  should  be  permitted.  In  other  words, 
it  is  not  the  carbon  dioxide  that  causes  the  injurious  re- 
sults, but  it  is  the  organic  matter  thrown  off  from  the 
body  in  the  expired  air :  the  carbon  dioxide  which  ac- 
companies the  organic  matter  is  only  the  index.  In 
testing  the  purity  of  the  air  it  is  easy  to  ascertain  the 
amount  of  carbon  dioxide  present,  and  very  difficult  to 
measure  the  amount  of  organic  matter ;  hence  it  is  the 
former  which  is  looked  for  in  lecture-rooms,  factories,  or 
churches,  and  when  it  is  found  to  exceed  0.07  per  cent,  it 
is  known  that  there  is  a  hurtful  amount  of  organic  matter 


RESPIRA  TION.  1 6  3 

present.  As  much  as  eighteen  times  the  normal  amount 
of  carbon  dioxide  has  been  found  in  school-rooms. 

To  maintain  the  air  sufficiently  pure  for  respiratory 
purposes,  90  cubic  metres  of  fresh  air  should  be  supplied 
per  hour  to  each  individual.  It  would  seem  to  be  an 
easy  thing  to  accomplish  this,  but  as  a  matter  of  fact  it 
is  one  of  the  most  difficult  problems.  To  supply  this 
amount  of  air  without  producing  such  draughts  as  to 
endanger  health  requires  that  to  each  individual  should 
be  allotted  a  certain  amount  of  air-space,  practically  not 
less  than  30  cubic  metres  per  person  in  health,  while  for 
the  sick,  as  in  hospitals,  double  this  amount  is  none  too 
great.  It  seems  hardly  necessary  to  say  that  due  atten- 
tion must  be  paid  to  the  source  from  which  the  intro- 
duced air  is  drawn.  If  it  be  taken  from  filthy  cellars  or 
from  dirty  streets,  it  may  be  as  impure  as  that  which  it 
is  designed  to  replace. 

CJianges  in  the  Blood  due  to  Respiration. — The  blood 
when  it  reaches  the  lungs  from  the  heart  is  venous,  and 
when  it  leaves  the  lungs  to  return  to  the  heart  it  is  arterial. 
The  conversion  of  the  venous  blood  into  arterial,  then, 
takes  place  while  the  blood  is  traversing  the  pulmonary 
capillaries.  As  previously  noted,  the  inspired  air  loses 
oxygen  during  its  stay  in  the  pulmonary  air-cells,  and 
arterial  blood  contains  more  oxygen  than  venous  blood  ; 
the  loss,  then,  which  the  air  sustains  is  a  gain  to  the 
blood.  The  expired  air,  while  it  contains  less  oxygen 
than  the  inspired  air,  contains  more  carbon  dioxide  and 
watery  vapor,  and  a  comparison  of  the  blood  going  to 
the  lungs  and  returning  from  them  shows  that  during  its 
passage  it  loses  these  very  ingredients. 

Internal  Respiration  is  the  process  by  which  the  tis- 
sues receive  oxygen  from  the  blood,  and  is  very  obscure. 


164  HUMAN  PHYSIOLOGY. 

There  are  no  means  of  ascertaining  just  how  much  oxy- 
gen is  taken  up  by  any  given  tissue  ;  it  is  only  known  that 
it  is  essential  this  gas  should  be  supplied  and  in  sufficient 
quantity,  and  that  when  this  does  not  occur  the  tissues 
suffer.  When  the  tissues  are  at  rest  the  amount  needed 
is  less  than  when  they  are  active,  but  under  the  latter 
condition  more  oxygen  is  eliminated  in  carbon  dioxide 
than  is  supplied  during  the  same  time,  showing  that 
when  at  rest  the  tissues  store  up  oxygen,  undoubtedly 
as  a  part  of  their  structure,  and  that  the  destructive 
changes  in  the  tissues  taking  place  to  a  greater  extent 
when  they  are  active  than  when  quiescent  result  in  the 
production  of  an  increased  amount  of  carbon  dioxide. 
This  is  true  of  all  activity,  both  that  of  glands  and  of 
muscles  as  well  as  of  other  structures. 

Respiration  is  a  process  of  oxidation,  the  principal 
product  of  which  is  carbon  dioxide.  The  oxygen  is  not 
converted  directly  into  carbon  dioxide,  but  becomes  an 
integral  part  of  the  tissues,  and  in  their  destructive 
metabolism  carbon  dioxide  is  one  of  the  products. 

4.  Vital  Heat. 

The  temperature  of  a  lifeless  object  is  approximately 
that  of  the  air  which  surrounds  it;  the  temperature 
of  a  living  object  is  independent  of  the  temperature 
of  the  air,  although  it  may  be  modified  by  it.  This 
difference  is  due  to  the  fact  that  living  things  pro- 
duce heat  within  themselves  :  this  is  called  "  vital  heat." 
Many,  perhaps  most,  authorities  speak  of  it  as  "  animal 
heat,"  but,  though  it  is  most  striking  in  members  of  the 
animal  kingdom,  yet  inasmuch  as  its  production  is  not 
confined  to  animals,  but  also  occurs  in  plants,  the  writer 
prefers  the  term  vital  heat  as  indicating  that  the  phenom- 


VITAL   HEAT.  1 65 

enon  is  peculiar  to  the  living  condition,  irrespective  of 
the  question  whether  it  occurs  in  an  animal  or  in  a  veg- 
etable. 

Warvi-bloodcd  Animals. — The  term  "  warm-blooded  " 
was  applied  to  certain  animals  because  their  temperature 
was  so  high  as  to  make  them  warm  to  the  touch,  while 
others  were  spoken  of  as  "  cold-blooded  "  because  they 
were  cold  to  the  touch.  Thus,  man  with  a  temperature 
of  37°  C.,  the  dog,  39°,  the  cat,  39°,  the  swallow,  44°  or 
even  higher,  are  among  the  warm-blooded,  while  reptiles 
and  fishes,  whose  temperature  is  from  1.70°  to  4.5°  C. 
above  that  of  the  medium  in  which  they  exist,  are  cold- 
blooded. The  terms  warm-blooded  and  cold-blooded 
are,  however,  now  not  so  frequently  used  as  formerly, 
but  in  their  stead  are  used  the  terms  homoiotJiennal  and 
poikilothennal. 

Hovioiothermal  animals  are  animals  of  uniform  heat  or 
whose  temperature  is  unvarying.  The  thermometer  if 
introduced  into  the  rectum  of  a  man,  whether  he  be  in 
the  tropics  or  in  the  frozen  regions  of  the  North,  will 
register  about  38°  C.  The  temperature  of  the  surface  of 
his  body  varies  with  that  of  the  air — a  fact  with  which 
all  are  familiar — but  the  internal  temperature  is  the  same, 
irrespective  of  whether  it  is  winter  or  summer.  What 
is  true  of  man  is  true  also  of  other  mammals  and  of  birds  ; 
that  is,  of  those  animals  commonly  denominated  warm- 
blooded. 

Poikilothennal  animals  are  animals  of  varying  heat,  or 
whose  temperature  varies  according  to  that  of  the  me- 
dium, air  or  water,  in  which  they  live.  The  frog's  tem- 
perature is  slightly  above  that  of  the  water,  and  if  this 
be  warmer  the  temperature  in  the  frog  will  rise,  to  fall 
again   when   the   temperature   of  the   water   is   lowered. 


1 66  HUMAN  PHYSIOLOGY. 

Fishes  also  exhibit  this  same  variation  of  temperature, 
so  that  cold-blooded  and  poikilothermal  are  practically 
interchangeable  terms.  A  study  of  insects  shows  that 
these  creatures  also  produce  heat,  the  thermometer  reg- 
istering, in  some  experiments  on  butterflies  in  active 
motion,  a  temperature  of  5°  C.  above  that  of  the  air. 
These  insects  are  poikilothermal.  The  same  power  of 
generating  heat  is  observed  also  in  plants.  The  amount 
of  heat  varies  under  different  circumstances,  being  espe- 
cially marked  at  the  time  of  germination  and  flowering, 
sometimes  from  5°  to  10°  C.  above  the  air. 

Heat-iinit. — The  standard  of  measure  of  heat  is  the 
heat-unit  or  calorie.  It  is  the  amount  necessary  to  raise 
the  temperature  of  i  gramme  of  water  i°  C.  A  kilo- 
calorie  is  equal  to  1000  calories,  and  it  represents  the 
amount  of  heat  necessary  to  raise  the  temperature  of  i 
kilogramme  (litre)  i°C.  It  is  estimated  that  an  average 
man  produces  daily  2500  kilo-calories,  which  is  about 
100  kilo-calories  per  hour.  During  active  exercise  this 
amount  is  greatly  increased,  even  to  the  amount  of  300 
kilo-calories  hourly,  while  during  sleep  it  is  only  40  kilo- 
calories. 

Sources  of  Heat. — The  sources  from  which  the  heat  of 
the  body  is  derived  are  as  follows : 

I.  The  oxidation  of  the  food-stuffs  is  one  of  the  im- 
portant sources  of  vital  heat — the  production  of  carbon 
dioxide  (CO2)  by  the  oxidation  of  the  carbon,  and  of 
water  (H2O)  from  the  hydrogen.  One  gramme  of  car- 
bon produces  8080  heat-units,  and  the  same  amount  of 
hydrogen  34,460  units.  The  oxygen  which  thus  com- 
bines with  these  elements  is  derived  from  the  air  during 
the  respiratory  process,  and  is  an  index  of  the  amount  of 
heat  produced.     That  is  to  say,  those  animals  have  the 


VITAL   HEAT.  1 6/ 

highest  temperature  that  consume  the  most  oxygen. 
The  oxidation  of  sulphur  and  phosphorus,  producing 
sulphuric  and  phosphoric  acids,  is  also  a  source  of  a 
little  heat.  While  oxidation  is  one  of  the  principal 
sources  of  heat,  many  of  the  other  chemical  processes 
taking  place  in  the  body  also  result  in  its  production. 

2.  Besides  the  chemical  causes  of  heat-production 
there  are  physical  causes.  Every  movement  which  occurs 
in  the  body  produces  some  heat ;  thus,  the  various  mus- 
cular contractions  contribute  largely  in  this  direction. 
Active  exercise  always  results  in  an  increase  of  heat- 
production — a  fact  which  is  made  use  of  when  the  body 
is  chilled  from  exposure. 

3.  The  changes  which  take  place  in  glands  during 
their  activity  are  still  another  source  of  heat.  This  is 
especially  noteworthy  in  the  liver,  the  blood  issuing 
from  which  has  the  highest  temperature  to  be  found 
anywhere  in  the  body. 

4.  A  factor  which  is  doubtless  of  no  great  importance 
in  contributing  to  heat-production  is  the  electricity  gen- 
erated in  muscles  and  nerves.  This  is  converted  into 
heat,  and  in  that  form  of  energy  leaves  the  body. 

Temperature  of  Different  Parts  of  the  Body. — The  tem- 
perature of  the  skin  at  the  middle  of  the  upper  arm  is 
35.4°  C,  while  in  the  sole  of  the  foot  it  is  but  32.26° 
C.  In  the  axilla  it  is  about  36.5°  C. ;  under  the  tongue, 
37.19°  C. ;  and  in  the  rectum,  38°  C.  The  mean  tem- 
perature of  the  blood  may  be  stated  as  39°  C.  The 
temperature  of  the  muscles  is  increased  in  contraction 
1°  C.  Mental  exertion  also  increases  the  production  of 
heat.  After  such  exertion  the  temperature  of  the  body 
has  been  found  to  be  0.3°  C.  higher  than  before. 

Temperature  at  Different  Ages. — The  temperature  of 


l68  HUMAN  PHYSIOLOGY. 

the  child  just  born  is  37.86°  C.  (rectum);  in  twenty-four 
hours,  37.45°  C.  (rectum).  From  five  to  nine  years  of 
age,  it  is  37.72°  C.  (rectum) ;  from  twenty-five  to  thirty, 
36.91°  C.  (axilla);  from  fifty-one  to  sixty,  36.83°  C. 
(axilla) ;  and  at  eighty,  37.46°  C.  (mouth).  The  amount 
of  heat  produced  in  old  people  is  less  than  that  in  the 
middle-aged,  and  they  therefore  need  greater  protection 
from  the  cold. 

Daily  Variations  in  Temperature. — The  temperature 
of  an  individual  is  not  the  same  at  all  times  of  the  day. 
His  lowest  temperature  is  between  2  and  6  o'clock  a.  m.; 
it  rises  during  the  day,  and  between  5  and  8  P.  m.  is  at 
its  height,  falling  again  until  it  reaches  the  minimum  in 
the  early  morning.  Thus,  in  one  set  of  observations,  at 
5  A.  M.  the  thermometer  registered  36.6°  ;  at  8  p.  m.,  37.7° 
C. ;  and  at  2  A.  m.  the  following  day,  36.7°  C.  If  the 
temperature  be  taken  every  hour  during  a  day,  the 
mean  of  the  readings  is  called  the  "  daily  mean,"  and  is 
about  37.13°  C.  in  the  rectum. 

Remarkable  Instances  of  High  and  Low  Temperature. 
— The  lowest  temperature  which  the  writer  has  been 
able  to  find  was  24°  C.  This  was  in  a  drunken  person 
who  recovered  from  his  debauch.  A  case  of  myxoedema 
is  reported  in  the  London  La?icet  in  which,  on  the  day 
previous  to  death,  the  temperature  varied  from  19°  C.  to 
25°  C.  In  the  same  journal  is  recorded  a  case  of  shock 
produced  by  a  fall  on  the  spine  in  which  the  temper- 
ature fluctuated  between  47°  C.  and  50°  C,  and  for  seven 
weeks  did  not  fall  below  42°  C. 

The  following  case,  recorded  in  the  Brooklyn  Med- 
ical jfournal,  illustrates  the  remarkable  variations  of 
temperature  which  may  take  place  in  a  few  hours.  The 
patient  was  a  man  aged  forty-eight;   the  diagnosis  of 


VITAL   HEAT.  1 69 

the  case  was  intermittent  fever.  He  had  been  treated 
two  or  three  months  before  for  delirium  tremens.  He 
left  the  hospital,  became  partially  paralyzed,  and  then 
developed  fever,  his  temperature  rising  to  42°  and 
45°  C. ;  May  i,  at  night,  it  was  44°  C. ;  May  2,  in 
the  morning,  37°  C. ;  May  4,  2  A.  m.,  44°  C.  He  had 
chills,  and  was  treated  for  malaria.  After  May  17  he 
had  no  rise  of  temperature.  He  was  a  wreck  from 
alcohol. 

Regulation  of  Temperature. — When  the  temperature 
of  the  muscles  is  raised  to  49°  C,  they  lose  their  con- 
tractility. This  figure  has  been  regarded  as  the  highest 
that  can  be  reached  by  a  living  human  being ;  indeed, 
much  below  this,  45°  C,  has  long  been  considered  as 
fatal,  although  a  temperature  of  nearly  52°  C.  has  been 
recorded.  When  the  temperature  falls  to  19°  C,  a  fatal 
result  will  follow. 

To  prevent  the  body  from  becoming  too  hot  is  one  of 
the  functions  of  the  skin.  This  it  accomplishes  by  ra- 
diation, conduction,  and  evaporation.  Of  the  total  heat 
given  off  from  the  body,  73  per  cent,  is  by  radiation  and 
conduction  from  the  skin,  and  14.5  per  cent,  is  by  evap- 
oration. Thus  there  is  carried  off  by  the  skin  nearly 
88  per  cent,  of  the  total  heat.  This  topic  will  again 
be  discussed  in  the  consideration  of  the  skin  and  its 
functions. 

The  prevention  of  the  reduction  of  the  temperature  of 
the  body  to  an  extent  that  would  be  harmful  is  accom- 
plished by  wearing  proper  clothing,  by  the  ingestion  of 
food,  both  solid  and  liquid,  by  warming  the  air  which 
comes  in  contact  with  the  body,  and  by  increased  mus- 
cular activity.  The  use  of  alcohol  for  this  purpose  is,  as 
previously  stated,  delusive. 


I/O  HUMAN  PHYSIOLOGY. 

5.  Circulation  of  the  Blood. 

The  blood,  in  carrying  nutrition  to,  and  in  carrying 
waste  products  from,  the  tissues,  makes  the  circuit  of 
the  circulatory  apparatus,  and  this  constitutes  circulation. 
The  circulatory  apparatus  consists  of  (i)  the  heart;  (2) 
the  arteries ;  (3)  the  capillaries ;  and  (4)  the  veins. 

TJie  heart  (Figs.  26,  27)  is  a  muscular  organ  whose 
functions  consist  in  acting  as  a  reservoir  and  also  as  a 
pump,  the  auricles  being  the  reservoir  and  the  ventricles 
being  the  pump  (PI.  2).  The  heart  has  a  conical  form, 
its  base  being  above  and  to  the  right,  and  its  apex  below 
and  to  the  left.  It  is  divided  longitudinally  by  a  parti- 
tion or  septum  into  a  right  and  left  half,  which  are  some- 
times denominated  the  right  heart  and  the  left  heart. 
Each  half  is  composed  of  an  auricle  and  a  ventricle ; 
thus  there  are  four  cavities — the  right  auricle,  the  right 
ventricle,  the  left  auricle,  and  the  left  ventricle. 

The  right  auricle  (Fig.  26)  is  somewhat  larger  than 
the  left,  and  has  the  thinnest  walls, of  the  four  cavities, 
measuring  about  2  mm.  in  thickness.  Discharging  into 
this  cavity  are  the  superior  and  the  inferior  vena  cava,  at 
the  mouths  of  which  there  are  no  valves.  Within  the 
cavity  is  the  Eustachian  valve,  which  will  further  be  de- 
scribed when  discussing  the  foetal  circulation.  This  valve 
is  situated  between  the  opening  of  the  inferior  vena  cava 
and  the  auriculo-ventricular  orifice. 

The  right  ventricle  (Fig.  26)  has  walls  whose  thickness 
is  greater  than  that  of  either  auricle,  but  is  less  than  that 
of  the  left  ventricle.  The  cavity  of  the  right  ventricle 
communicates  with  that  of  the  right  auricle  by  the  right 
auriculo-ventricular  orifice,  at  which  is  situated  the  tri- 
cuspid valve.  It  ordinarily  contains,  when  filled,  180 
grammes  of  blood.     Connected  with  this  ventricle  is  the 


PLATE    II 


A,  aorU,  with  left  vagus  and  phrenic  nerves  crossing  its  transverse  arch;  B,  root 
of  pulmonary  artery;  C,  right  ventricle,  /;,  right  auricle  E,  vena  cava  superior, 
with  right  phrenic  nerve  on  its  outer  border  ;  /',  F,  right  and  left  lungs  collapsed,  and 
turned  outward  to  show  the  heart's  outline  ;  6",  inferior  vena  cava  ;  //,  cceliac  axis, 
dividing  into  the  gastric,  splenic,  and  hepatic  arteries. 


CIRCULATION  OF  BLOOD. 


171 


pulmonary  artery,  at  whose  point  of  junction  with  the 
ventricle  is  the  pulmonary  orifice,  at  which  is  situated 
the  pulmonary  valve. 


Fig.  26. — Interior  of  Right  Auricle  and  Ventricle,  exposed  by  the  removal  of  a  part 
of  their  walls  (Allen  Thomson)  :  i,  superior  vena  cava;  2,  inferior  vena  cava;  2',  he- 
patic veins;  3,3',  3",  inner  wall  of  right  auricle;  4,4,  cavity  of  right  ventricle;  4',  papil- 
lary muscle;  5,  5',  5",  flaps  of  tricuspid  valve  ;  6,  pulmonary  artery,  in  the  wall  of 
which  a  window  has  been  cut :  7,  on  aorta  near  the  ductus  arteriosus  ;  8,  9,  aorta  and 
its  branches;  10,  11,  left  auricle  and  ventricle. 

The  left  auricle  (Fig.  27)  is  not  so  large  as  the  right, 
but  its  walls  are  thicker.  Discharging  into  it  are  the 
two  right  and  the  two  left  pulmonary  veins,  the  former 
coming  from  the  right  and  the  latter  from  the  left  lung. 
The  left  veins  sometimes  join,  and  have  but  a  single 
opening,  in  which  case  there  would  of  course  be  but 
three  openings  instead  of  four.  At  these  openings  there 
are  no  valves. 


172 


HUMAN  PHYSIOLOGY. 


The  left  ventricle  (Fig.  27)  is  by  far  the  most  powerful 
of  the  four  subdivisions  of  the  heart.    Its  walls  are  three 

times  as  thick  as  those  of  the 
right  ventricle.  The  capacity 
of  its  cavity  is  the  same  as  that 
of  the  right.  The  left  auricle 
and  ventricle  communicate  by 
the  left  auriculo-ventricular 
orifice,  at  which  is  situated  the 
mitral  valve.  Connected  with 
this  ventricle  is  the  aorta,  the 
opening  of  communication  be- 
ing the  aortic  orifice,  at  which 
is  situated  the  aortic  valve. 

On  the  inner  surface  of  the 
ventricles  the  muscular  tissue 
projects,  and  forms  the    co- 
lumnae  carneae,  or  fleshy  col- 
umns ;    some    of    these    are 
ridges    only,    while     others 
Left  Auricle  .ind  Ventricle,  arc   attached    at   both    cuds, 
but    are    unattached    in    the 
while     still     others 
thick  wall  ofieft  ventricle;  4,  portion  project   into    thc    cavity  and 

are  attached  at  one  ex- 
tremity only ;  the  latter  are 
the  musculi  papillares,  or 
papillary  muscles. 
Cardiac  Valves. — There  are  four  sets  of  valves  in  the 
heart:  (i)  The  tricuspid;  (2)  the  pulmonary;  (3)  the 
mitral ;  and  (4)  the  aortic.  The  tricuspid  valve  (Fig.  28) 
is  situated  at  the  right  auriculo-ventricular  orifice,  and, 
as  its  name  implies,  consists  of  three  cusps  or  segments. 


Fig.    27. 
opened  and  part  of  their  walls  removed 
to   show  their   cavities    (Allen  Thom- 
son) :    I,    right    pulmonary    vein    cut   flliddlc 
short ;  i',  cavity  of  left  auricle  ;  3,  3" 
)ortic 
of  the  same  with  papillary  muscle  at- 
tached; 5,  the  other  papillary  muscles  ; 

6,  6',  the  segments  of  the  mitral  valve  ; 

7,  in  aorta  is  placed  over  the  semilunar 
valves;  8,  pulmonary  artery;  10, 
aorta  and  its  branches. 


CIRCULATION  OF  BLOOD. 


^7Z 


The  bases  of  these  cusps  are  attached  to  the  opening, 
while  the  other  edges  are  free,  and  to  them  are  attached 
the  chordae  tendineae,  or 
tendinous  cords,  the  other 
ends  being  connected 
with  the  free  extremities 
of  the  musculi  papillares 
above  referred  to.  This 
valve,  when  shut,  closes 
the  right  auriculo-ven- 
tricular  orifice ;  when 
open,  the  segments  are 
in  the  cavity  of  the  right 
ventricle.  The  tendinous 
cords  prevent  these  seg- 
ments from  passing  into 
the  cavity  of  the  auricle 
at  the  time  of  the  valve's 
closure,  while  the  papillary  muscles  by  their  contraction 
keep  the  cords  taut  at  the  time  of  the  ventricle's  con- 
traction, as  will  be  seen  later. 

The  pul7)ionary  valve  is  sometimes  spoken  of  as  the 
"  pulmonary  semilunar  valve "  or  valves.  It  is  com- 
posed of  three,  occasionally  of  two,  segments,  and  is 
situated  at  the  beginning  of  the  pulmonary  artery. 
These  segments  are  attached  at  their  bases  to  the  wall 
of  the  artery,  and  on  the  free  edge  of  each  is  a  pro- 
jection called  corpus  Arantii.  When  the  valve  is  open 
the  segments  lie  against  the  walls  of  the  artery ;  when  it 
is  shut,  they  are  in  contact,  and  thus  close  the  orifice  of 
the  pulmonary  artery. 

The  mitral  valve  is  also  described  as  the  bicuspid,  be- 
cause it  consists  of  two  cusps.     The  attachments  of  the 


Fic.  28. — Orifices  of  the  Heart,  seen  from 
above,  both  the  auricles  and  the  great  ves- 
sels being  removed  (Huxley) :  PA,  pulmo- 
nary artery  and  its  semilunar  valves;  AO, 
aorta  and  its  valves ;  RA  V,  tricuspid,  and 
LAV,  bicuspid  valves;  MV,  segments  of 
mitral  valve;  LV,  segments  of  tricuspid 
valve. 


174  HUMAN  PHYSIOLOGY. 

segments,  the  presence  of  chordae  tendineae,  and  the 
other  anatomical  points  referred  to  in  speaking  of  the 
tricuspid  valve  are  to  be  seen  in  connection  with  the 
mitral.     It  closes  the  left  auriculo-ventricular  orifice. 

The  aortic  valve  resembles  in  all  essential  particulars 
the  pulmonary ;  it  likewise  is  sometimes  called  the 
"semilunar  valve,"  and  closes  the  aortic  orifice.  The 
ventricular  septum  is  the  partition  between  the  right 
and  the  left  ventricles.  It  is  at  all  periods  of  life  closed. 
The  auricular  septum,  between  the  auricles,  is  closed 
from  the  tenth  day  after  birth  ;  prior  to  this  time  and 
during  foetal  life  it  has  an  opening,  the  foramen  ovale, 
which  serves  as  a  means  of  communication  between  the 
right  and  the  left  auricles. 

The  arteries  are  composed  of  three  coats — an  internal, 
a  middle,  and  an  external.  The  middle  coat  has  a  spe- 
cial physiological  interest.  In  the  large  arteries — that 
is,  those  larger  than  the  carotids — this  coat  is  principally 
yellow  elastic  tissue,  only  about  one-fourth  being  mus- 
cular tissue.  Vessels  of  this  size  are  therefore  charac- 
terized by  their  elasticity.  In  the  arteries  of  medium 
size — that  is,  those  between  the  carotids  and  those  hav- 
ing a  diameter  of  2  mm. — the  amount  of  muscular  tis- 
sue is  very  much  increased,  while  the  elastic  tissue  is 
also  well  represented.  Such  arteries  possess,  therefore, 
both  contractility  and  elasticity.  In  the  small  arteries — 
that  is,  those  less  than  2  mm.  in  diameter — the  external 
coat  gradually  disappears  until  in  the  arterioles  there  re- 
mains only  muscular  tissue,  representing  the  middle  coat 
and  the  internal  coat.  These  vessels  are  endowed  with 
the  property  of  contractility. 

Tlie  capillaries  are  minute  vessels,  being,  on  an  average, 
16  m.mm.  in  diameter.     In  some  tissues,  as  in  the  brain, 


CIRCULATION  OF  BLOOD.  1 75 

they  are  smaller,  while  in  the  skin  they  are  larger.  They 
are  composed  of  endothelial  cells  joined  edge  to  edge, 
and  are  exceedingly  thin.  From  a  physiological  stand- 
point this  system  of  vessels  is  the  most  important  part 
of  the  circulatory  apparatus. 

The  Veins. — The  structure  of  the  veins  is  in  many  re- 
spects similar  to  that  of  the  arteries.  They  are  likewise 
composed  of  three  coats,  but  the  middle  coat  is  thinner 
— so  much  so,  indeed,  that,  while  the  arteries  when  cut 
remain  patulous,  the  veins  collapse.  This  coat  contains 
both  elastic  and  fibrous  tissue:  the  former  gives  these 
vessels  some  elasticity,  while  to  the  latter  is  attributable 
the  greater  strength  of  the  veins  as  compared  with  the 
arteries.  The  greater  thickness  of  the  arterial  wall  would 
seem  calculated  to  make  these  vessels  the  stronger,  but, 
although  possessed  of  thin  walls,  still  the  white  fibrous 
tissue  which  aids  in  their  formation  gives  the  veins 
greater  resisting  power.  Valves  are  to  be  found  in 
most  of  the  veins,  but  are  absent  in  those  whose  diam- 
eter is  less  than  2  mm. ;  also  from  the  venae  cavae,  hepatic, 
portal,  renal,  uterine,  ovarian,  cerebral,  spinal,  pulmo- 
nary, and  umbilical  veins.  The  valves  are  so  arranged 
that  they  permit  the  blood  to  flow  in  the  direction  of  the 
heart,  but  prevent  its  flow  in  the  opposite  direction. 

Circulation  of  the  Blood. — The  course  of  the  blood, 
starting  from  any  point,  may  be  traced  through  the  cir- 
culatory apparatus.  Beginning  with  the  right  auricle, 
the  blood  flows  into  this  cavity  from  the  venae  cavae 
(inferior  and  superior) ;  thence  through  the  right  auric- 
ulo-ventricular  orifice  into  the  right  ventricle ;  thence 
into  and  through  the  pulmonary  artery  to  the  lungs; 
thence  by  the  pulmonary  veins  into  the  left  auricle ; 
thence  through  the  left  auriculo-ventricular  orifice  into 


1/6  HUMAN  PHYSIOLOGY. 

the  left  ventricle ;  thence  into  and  through  the  aorta  and 
the  arterial  system  to  the  capillaries ;  through  these  ves- 
sels to  the  veins,  by  which  it  returns  to  the  right  auricle, 
the  place  of  beginning. 

Cardiac  Movements. — If  the  heart  be  exposed  in  a  liv- 
ing animal — a  dog,  for  example — it  will  be  seen  that  the 
ventricles  are  at  one  time  in  motion  and  at  another  time 
at  rest.  Each  period  of  motion  and  rest  constitutes  a 
"  pulsation "  or  a  cardiac  cycle,  and  these  pulsations 
recur  very  rapidly,  so  much  so  that  the  intervals  are 
recognized  with  difficulty.  These  different  states  of  the 
heart  are  better  detected  by  the  sense  of  touch  than  by 
that  of  sight.  If  the  ventricles  be  grasped  by  the  hand, 
it  will  be  found  that,  corresponding  with  the  resting 
stage,  the  muscular  tissue  composing  them  is  soft  and 
flaccid,  while  during  the  active  stage  it  is  hard  and  re- 
sisting. If  these  movements  be  studied  still  more  care- 
fully and  analyzed,  it  will  be  found  that  the  beginning 
of  the  cardiac  movement,  which  immediately  follows  the 
stage  of  rest,  occurs  in  the  auricles,  in  the  region  of  the 
openings  of  the  venae  cavae  on  the  right  side,  and  in 
the  pulmonary  veins  on  the  left ;  that  this  movement  is 
propagated  along  the  auricles  in  the  direction  of  the  ven- 
tricles ;  and  that  by  the  time  it  has  reached  the  auriculo- 
ventricular  orifices  it  has  ceased  at  the  orifices  of  the 
veins,  and  the  muscular  tissue  in  this  region  has  begun 
to  relax.  It  is  to  be  noted  that  the  auricles  act  syn- 
chronously, so  that  whatever  is  the  condition  of  one 
auricle  as  to  relaxation  or  contraction  of  its  muscular 
tissue,  the  same  condition  exists  in  the  other.  This  con- 
traction of  the  auricles  is  spoken  of  as  the  "  auricular 
systole,"  and  has  something  of  the  peristaltic  character, 
which  has  already  been  studied  in  the  stomach  and  small 


CIRCULATION  OF  BLOOD.  1 77 

intestine,  although  differing  very  materially  in  that  it  is 
much  more  rapid. 

Up  to  this  time  the  ventricles  have  been  relaxed,  or  in 
a  condition  of  diastole,  but  as  soon  as  the  auricular  con- 
traction reaches  the  ventricles  these  organs  take  it  up, 
although  in  a  different  manner.  For,  while  in  the  aur- 
icles one  portion  is  contracting  while  another  is  relax- 
ing, in  the  ventricles  the  whole  mass  of  muscle  con- 
tracts at  once  with  a  degree  of  suddenness  and  vigor 
which  might  be  expected  of  so  large  a  mass  of  striped 
muscular  tissue.  This  contraction  is  the  "  ventricular 
systole,"  and  while  it  is  taking  place  the  auricles  are 
relaxing  throughout ;  this  relaxation  constitutes  the 
"auricular  diastole."  Thus  the  auricular  systole  and 
ventricular  diastole,  and  the  auricular  diastole  and 
ventricular  systole,  are  respectively  synchronous.  Im- 
mediately after  the  systole  of  the  ventricles  these  struc- 
tures relax,  and  for  a  brief  period  the  whole  heart,  both 
auricles  and  both  ventricles,  is  in  a  state  of  relaxation ; 
this  is  the  "pause"  of  the  heart.  The  work  performed 
by  the  ventricles  is  so  much  more  important  than  that 
of  the  auricles  that  when  the  terms  systole  and  diastole 
are  used  reference  is  always  had  to  these  states  of  the 
ventricles,  the  auricles  being  practically  ignored.  To 
designate  the  corresponding  states  of  the  auricles  it  is 
always  neces.sary  to  speak  of  the  auricular  systole  and 
diastole. 

Movements  of  Blood  dtiring  Systole  and  Diastole. — Be- 
fore considering  other  movements  of  the  heart  it  will  be 
well  to  study  the  course  of  the  blood  while  contraction 
and  relaxation  of  the  muscular  tissue  of  this  organ  are 
taking  place. 

The  venous  blood,  returning  from  the  head  and  upper 
12 


178  HUMAN  PHYSIOLOGY. 

extremities  by  the  superior  or  descending  vena  cava,  and 
from  the  portion  of  the  body  below  the  heart  by  the  infe- 
rior or  ascending  vena  cava,  flows  into  and  through  the 
right  auricle,  passing  into  the  right  ventricle  through 
the  right  auriculo-ventricular  orifice.  The  tricuspid 
valve  at  this  time  is  open,  and  offers  no  obstacle  to  the 
passage  of  the  blood.  More  blood  enters  the  auricles 
than  can  at  once  pass  out  of  them  into  the  ventricles ; 
consequently  some  blood  accumulates  in,  and  gradually 
fills,  the  auricles,  although  at  the  same  time  as  much 
blood  is  flowing  into  the  ventricles  as  the  auriculo-ven- 
tricular orifices  will  permit  to  pass,  nearly  filling  these 
cavities,  and  floating  up  the  segments  of  the  mitral  and 
tricuspid  valves  until  they  are  nearly  closed.  This  is 
the  condition  at  the  end  of  the  pause.  At  this  moment 
begins  the  auricular  systole.  Near  the  ends  of  the  veins 
which  discharge  into  the  auricles — that  is,  the  venae 
cavae  and  pulmonary  veins — are  muscular  fibres :  these 
fibres  contract,  diminishing  the  size  of  the  orifices  of  the 
veins,  thus  taking  the  place  of  valves,  and  partially  pre- 
venting regurgitation  or  a  back-flow  of  blood  into  these 
vessels.  Then  the  muscular  fibres  of  the  auricles  in 
contiguity  with  these  fibres  contract,  the  motion  spread- 
ing to  the  adjoining  fibres  until  the  wave  of  contraction 
has  reached  the  ventricles.  This  auricular  contraction 
forces  more  blood  into  the  ventricles,  and  as  the  fibres 
relax  the  blood  enters  the  auricles  again  from  the  veins. 
It  will  thus  be  seen  that  the  interval  during  which  the 
venous  flow  is  arrested  is  the  briefest  time  possible.  The 
principal  office  of  the  auricles  is  to  serve  as  reservoirs  to 
supply  the  ventricles;  the  work  they  do  in  completing 
the  filling  of  these  cavities  is  comparatively  unimportant. 
The  auricular  systole  is  followed  by  the  systole  of  the 


CIRCULATION  OF  BLOOD.  1 79 

ventricles.  These  cavities  are  at  this  time  filled  with  blood, 
and  the  auriculo-ventricular  valves  are  nearly  closed,  the 
segments  having  been  raised  up  by  the  blood  from  the 
auricles.  The  ventricles,  as  has  been  stated,  contract  en 
masse,  and  the  blood  which  they  contain  is  compressed 
with  great  force.  Under  the  pressure  it  tends  to  escape 
from  the  ventricles  by  all  outlets — on  the  right  side  by 
the  right  auriculo-ventricular  orifice  back  into  the  right 
auricle,  and  by  the  pulmonary  orifice  into  the  pulmonary 
artery;  on  the  left  side  by  the  left  auriculo-ventricular 
orifice  into  the  left  auricle,  and  by  the  aortic  orifice  into 
the  aorta.  The  pressure  of  the  blood  instantly  closes 
the  tricuspid  valve,  and  thus  prevents  the  blood  from 
going  back  into  the  right  auricle.  The  same  force 
closes  the  mitral  valve,  and  the  regurgitation  of  blood 
into  the  left  auricle  is  made  impossible.  The  pulmonary 
and  aortic  valves,  as  has  been  stated,  open  from  the  ven- 
tricles into  the  arteries.  At  the  beginning  of  the  ven- 
tricular systole  the  valves  are  closed,  but  when  this 
occurs  the  pressure  of  the  blood  forces  them  open,  and 
the  contents  of  the  ventricles,  180  grammes  for  each,  are 
propelled  into  the  pulmonary  artery  and  the  aorta  re- 
spectively. In  accomplishing  this  injection  the  ven- 
tricles have  to  overcome  the  pressure  which  the  blood 
already  in  the  arteries  is  exerting  on  the  other  side  of 
the  valves  to  keep  them  closed.  This  pressure  in  the 
aorta  is  equal  to  a  column  of  mercury  200  mm.  high, 
and  in  the  pulmonary  artery  is  one-third  as  much.  The 
amount  of  work  done  by  the  ventricle  daily  in  thus 
forcing  blood  into  the  arteries  is  equal  to  that  which  is 
performed  by  an  individual  weighing  75  kilogrammes 
in  climbing  a  mountain  806  metres  in  height. 

As  soon  as  the  ventricles  cease  their  contraction  the 


l8o  HUMAN  PHYSIOLOGY. 

pressure  of  the  blood  in  the  arteries  closes  the  pulmon- 
ary and  aortic  valves,  the  ventricles  begin  their  diastole, 
and  the  pause  of  the  heart  commences.  As  it  was  at 
this  point  that  the  consideration  of  the  changes  which 
take  place  was  begun,  the  study  of  a  cardiac  cycle,  car- 
diac period,  or  heart-beat  is  now  completed.  If  the 
time  occupied  by  such  a  period  be  divided  into  one  hun- 
dred parts,  it  will  be  found  that  the  auricular  systole 
lasts  during  nine  of  the  parts,  the  ventricular  systole 
during  thirty,  and  the  pause  during  sixty-one ;  or,  in 
other  words,  the  heart  is  at  rest  six-tenths  and  at  work 
four-tenths  of  the  time. 

SJiortening  of  the  Heart. — At  the  time  of  the  systole 
of  the  heart  (ventricular  systole)  the  organ  becomes 
shorter,  yet  the  apex  does  not  change  its  place,  for  the 
lengthening  of  the  aorta  which  occurs  compensates  for 
the  shortening,  so  that  while  the  apex  and  base  approx- 
imate the  whole  heart  is  lowered,  the  result  being  to 
keep  the  apex  in  its  original  position  with  reference  to 
the  chest- wall. 

Cm'diac  Impulse. — The  situation  of  the  heart  in  the 
thoracic  cavity  is  such  that  its  apex  is  against  the  chest- 
wall  at  the  fifth  intercostal  space,  the  space  between  the 
fifth  and  sixth  ribs,  and  an  inch  and  a  half  below  and  half 
an  inch  within  the  left  nipple.  The  apex  of  the  heart  is 
the  extreme  point  of  the  left  ventricle.  If  the  finger  be 
placed  in  this  region  during  the  ventricular  systole,  there 
will  be  felt  a  tap  as  if  something  were  gently  striking  it. 
This  tap  is  known  as  the  "  apex-beat."  It  was  so  called 
because  it  was  formerly  supposed  that  during  the  sys- 
tole the  heart  was  raised  up  and  so  carried  forward  as  to 
cause  the  apex  to  strike  against  the  chest- wall  and  thus 
to  produce  this  sensation.     A  more  careful  study  of  the 


CIRCULATION  OF  BLOOD.  l8l 

changes  which  the  heart  undergoes  during  systole  has, 
however,  demonstrated  that  the  apex  of  the  heart  is 
always  in  contact  with  the  chest-wall,  and  that  this  sup- 
posed striking  does  not  take  place.  Indeed,  the  tap  is 
not  due  to  the  apex  at  all.  The  term  apcx-bcat  is  a  mis- 
nomer :  it  should  rather  be  called  a  "  cardiac  impulse," 
the  sensation  being  produced  by  the  anterior  surface  of 
the  contracting  ventricles  swelling  out  and  hardening. 
The  location  at  which  this  impulse  is  felt  most  pro- 
nouncedly is  not  over  the  apex,  but  higher  up.  If  a 
long  needle  were  to  be  introduced  deeply  at  this  point, 
it  would  penetrate  the  left  ventricle  at  a  point  where  the 
middle  and  lower  thirds  unite.  The  cardiac  impulse  is 
not  always,  even  in  health,  detected  at  the  same  place  : 
it  changes  somewhat  with  respiration  and  also  with 
changes  in  the  position  of  the  body. 

Papillary  Muscles. — It  has  been  stated  that  during  the 
ventricular  systole  the  heart  shortens.  It  is  manifest 
that  unless  some  provision  were  made  this  change  in 
the  shape  of  the  heart  would  permit  of  regurgitation  of 
the  blood  into  the  auricles,  and  thus  would  result  a  dam- 
ming back  of  the  blood  in  the  venae  cavae  and  pulmonary 
veins;  for  if  the  chordae  tendineae  were  of  just  the  right 
length  at  the  beginning  of  the  ventricular  systole  to  keep 
the  segments  of  the  mitral  and  tricuspid  valves  so  exactly 
in  place  as  not  to  permit  a  leakage,  then  when  the  ven- 
tricles shortened  these  cords  would  be  too  long,  and 
would  permit  the  segments  to  enter  the  cavity  of  the 
auricles  and  thus  separate,  leaving  a  considerable  gap 
through  which  the  blood  could  pass.  That  this  docs  not 
occur  is  due  to  the  papillary  muscles.  As  the  ventricles 
shorten  these  structures  contract  sufficiently  to  take  up 
the  slack  in  the  cords,  and  keep  them  just  long  enough 


1 82  HUMAN  PHYSIOLOGY. 

to  maintain  the  proper  approximation  of  the  segments 
of  the  valves. 

Cardiac  Sounds. — When  the  ear  is  placed  against  the 
chest-wall  in  the  region  of  the  heart,  two  sounds  are 
heard  during  each  cardiac  period.  The  first  of  these 
sounds  is  heard  loudest — that  is,  at  its  maximum  of  in- 
tensity— over  the  apex,  and  is  by  some  writers  called  the 
"  apex-sound."  For  the  reason  that  it  is  the  first  sound 
heard  after  the  pause  it  is  called  the  "  first  sound,"  and 
because  it  occurs  at  the  beginning  of  the  systole  of  the 
heart  (ventricular  systole)  it  is  called  the  "  systolic 
sound."  The  second  sound  is  heard  loudest  over  the 
base  of  the  heart,  and  is  therefore  sometimes  described 
as  the  "  basic  sound  ;"  inasmuch  as  it  occurs  during  the 
diastole,  it  has  received  the  name  of  the  "  diastolic 
sound."  More  commonly,  however,  it  is  spoken  of  as 
the  "second  sound." 

Characteristics  of  the  Cardiac  Sounds. — The  first  sound, 
as  compared  with  the  second,  is  lower  in  pitch  and  longer 
in  duration,  and  has  been  likened  to  the  sound  of  the 
word  lubb.  The  second  sound  is  higher  in  pitch  and 
shorter  in  duration  than  the  first,  and  has  been  likened 
to  the  sound  of  dup.  These  sounds  occur  successively, 
without  any  interval  between  them  ;  in  the  pause  which 
follows  no  sound  is  heard. 

Causes  of  the  Cardiac  Sounds. — The  cause  of  the 
second  sound  is  undoubtedly  the  closure  of  the  aortic 
and  pulmonary  valves.  This  has  been  demonstrated  by 
hooking  back  the  segments  of  the  valves,  when  the  sound 
disappeared,  to  reappear  when  the  segments  were  set 
free.  The  causation  of  the  first  sound  is  not  so  simple  ; 
indeed,  authorities  are  not  at  one  on  this  point.  The 
closure  of  the  mitral  and  tricuspid  valves  contributes 


CIRCULATION  OF  BLOOD.  1 83 

something  to  it,  but  the  closing  of  the  valves  is  not  the 
sole  factor,  for  in  a  heart  in  which  there  is  no  blood  the 
sound  may  still  be  heard,  although  modified,  and  in  such 
a  heart  the  valves  would  not  close.  The  contraction  of 
the  muscular  tissue  of  the  heart  gives  forth  a  sound,  as 
does  indeed  the  contraction  of  other  muscles,  and  this 
is  also  an  element  in  producing  the  first  sound.  The 
striking  of  the  apex  against  the  chest-wall,  the  so-called 
apex-beat,  formerly  regarded  as  one  of  the  factors  of  the 
first  sound,  can  take  no  part  in  its  production,  because, 
as  has  been  pointed  out,  this  action  does  not  take  place. 

Every  student  should  familiarize  himself  with  the  car- 
diac sounds,  not  simply  by  reading  about  them  in  books, 
but  by  listening  to  the  human  chest.  A  thorough  know- 
ledge of  their  character  is  essential  to  a  comprehension 
of  the  diseases  of  the  heart.  It  is  important  to  remem- 
ber that  the  impulse  of  the  heart,  the  systole  of  the  ven- 
tricles, the  first  sound,  and  the  closure  of  the  mitral  and 
tricuspid  valves  are  synchronous,  and  that  when  the 
second  sound  is  heard  the  ventricles  are  beginning  their 
diastole  and  the  aortic  and  pulmonary  valves  have  just 
closed. 

Circulation  in  the  Arteries  (Fig.  33). — Each  time  that 
the  ventricles  contract  they  send  into  the  arteries  360 
grammes  of  blood,  each  ventricle  expelling  180  grammes. 
The  arterial  system  is  always  over-distended  ;  that  is,  even 
when  the  heart  is  at  rest  the  amount  of  blood  in  the 
arteries  is  enough  to  stretch  their  walls  a  little.  When 
an  additional  amount  of  blood  is  forced  into  them  by 
the  muscular  contraction  of  the  heart,  these  vessels  are 
distended  still  more,  for  the  blood  already  in  them  can- 
not at  once  flow  on  in  an  amount  equal  to  that  which 
comes  from  the  heart.     If  an  artery  at  this  time  should 


184  HUMAN  PHYSIOLOGY. 

be  felt  with  the  finger,  it  would  beat  against  the  latter, 
this  beat  being  the  pulse.  As  soon  as  the  systole  ceases 
the  elastic  coats  of  the  arteries  squeeze  the  blood  within 
them,  and  this  blood  tends  to  flow  away  from  the  point 
of  pressure  in  two  directions — back  toward  the  heart 
and  onward  toward  the  capillaries.  Its  backward  flow 
at  once  closes  the  pulmonary  and  aortic  valves,  and  in 
this  direction,  therefore,  its  progress  is  barred.  The  blood 
then  can  only  go  forward.  Before  the  onward  flow  of 
the  blood  has  ceased  another  systole  occurs,  and  again 
the  ventricles  are  emptied  into  the  arteries,  and  thus  con- 
tinues this  action  during  the  life  of  the  individual.  If  a 
cannula  be  inserted  into  the  cavity  of  the  ventricle,  it  will 
be  seen  that  at  each  systole  the  blood  spurts  out  in  a  jet, 
which  ceases  at  the  end  of  the  systole ;  that  is,  the  flow 
from  the  heart  is  intermittent.  If  the  cannula  be  inserted 
into  the  aorta,  the  blood  will  jet  out  at  each  systole  of  the 
heart,  but,  instead  of  ceasing  to  flow  during  diastole,  it 
will  not  entirely  cease,  but  will  continue  to  flow  a  little 
under  the  influence  of  the  elastic  force  of  the  aorta.  If 
the  cannula  be  inserted  into  successive  portions  of  the 
arterial  system  farther  and  farther  from  the  heart,  the 
blood  will  come  out  in  jets  as  before  under  the  influence 
of  the  heart's  contraction,  but  it  will  continue  to  flow  in 
the  intervals,  the  difference  between  the  jet  and  the  con- 
tinuous flow  being  less  and  less  marked  the  greater  is 
the  distance  of  the  insertion  of  the  cannula  from  the 
heart.  In  the  capillaries  the  flow  is  regular  and  con- 
tinuous, unaffected  by  the  action  of  the   heart. 

Internal  Friction. — If  the  blood  be  studied  as  it  is  flow- 
ing through  a  small  artery  in  the  web  of  a  frog's  foot,  it 
will  be  seen  that  in  the  centre  of  the  current  it  is  flowing 
much  faster  than  at  the  sides ;  this  is  the  "  axial  stream," 


CIRCULATION  OF  BLOOD.  185 

and  in  it  will  be  observed  the  red  corpuscles.  That  por- 
tion of  the  current  which  is  between  the  axial  stream 
and  the  walls  of  the  vessel  moves  more  slowly,  the  rate 
diminishing  from  the  centre  outward,  until  at  the  walls 
themselves  it  is  at  the  minimum.  This  outer  portion  is 
known  as  the  "  inert  layer."  It  should  be  stated  that 
this  arrangement  of  the  current  is  not  due  to  any  pecu- 
liarity of  the  blood  or  of  the  vessels  through  which  it 
flows,  but  is  present  in  every  fluid  while  flowing  through 
a  tube.  Between  the  different  layers  of  fluid  there  is 
friction,  called  "  internal  friction."  The  smaller  the  tubes 
the  greater  the  internal  friction,  so  that  the  amount  of 
friction  in  the  subdivisions  of  the  aorta  and  the  larger 
arteries  and  in  the  capillaries  is  very  great,  and  this  fric- 
tion acts  as  an  obstacle  to  the  outflow  of  the  blood,  con- 
stituting peripheral  resistance. 

Arterial  Pressure. — If  a  U-tube  containing  mercury  be 
connected  with  an  artery,  the  mercury  will  rise  in  the 
distal  end  under  the  influence  of  the  pressure  on  the 
other  end  of  the  blood  on  the  column.  This,  then,  will 
indicate  the  arterial  pressure ;  that  is,  the  pressure  under 
which  the  blood  is  in  the  arteries.  In  the  aorta  it  is 
equal  to  a  column  of  mercury  200  mm.  in  height.  At 
the  time  of  the  sy.stole  it  will  be  5  mm.  more.  In  the 
pulmonary  artery  the  pressure  is  one-third  that  in  the 
aorta. 

Rate  of  Floiv  in  the  Arteries. — It  has  been  calculated 
that  in  the  carotid  artery  of  a  man  the  blood  flows  at 
the  rate  of  400  mm.  per  second.  Inasmuch  as  the 
capacity  of  the  arterial  system  increases  as  the  arteries 
divide,  the  current  in  the  smaller  arteries  will  be  slower 
than  in  the  larger ;  in  the  metatarsal  artery  one  observer 
found  it  to  be  but  56  mm. 


1 86 


HUMAN  PHYSIOLOGY. 


Pulse-tvave. — The  rate  at  which  the  blood  flows  and 
that  at  which  the  pulse-wave  moves  are  two  different 
quantities.  In  the  former  case  we  are  dealing,  as  it 
were,  with  the  velocity  of  the  same  portions  of  the  blood 
or  the  same  individual  corpuscles.  In  the  latter  case  we 
are  dealing  with  a  wave  which  starts  at  the  aortic  valve 
and  is  propagated  through  the  entire  mass  of  arterial 
blood  ;   manifestly  the   rate  of  the  latter  will  be  much 


Fig.  29. — Normal  Vessels  and  Blood-stream  (Landerer)  :  a,  artery;  b,  vein; 
c ,  capillary. 


faster.  At  the  commencement  of  the  aorta  the  wave 
begins;  in  0.159  seconds  it  will  be  felt  at  the  wrist,  and 
in  0.193  seconds  at  the  ankle.  It  travels  at  the  rate  of 
9  metres  per  second. 


CIRCULATION  OF  BLOOD.  1 87 

Circidation  in  the  Capillaries  (Fig.  29). — The  forces 
which  propel  the  blood  through  the  arteries — namely, 
the  contractile  force  of  the  ventricles  and  the  elastic 
force  of  the  arteries,  collectively  called  the  vis  a  tergo — 
are  sufficient  to  carry  the  blood  on  through  the  capil- 
laries. The  sectional  area  of  the  capillaries  is  seven 
hundred  times  greater  than  that  of  the  aorta,  so  that 
the  blood  which  flows  through  this  latter  vessel  at  the 
rate,  perhaps,  of  500  mm.  per  second  is,  when  it  reaches 
the  capillaries,  so  widely  distributed  that  its  flow  is 
very  much  reduced  in  rapidity — only  about  i  mm.  per 
second. 

It  is  while  passing  through  the  capillary  .system  that 
the  important  interchanges  take  place  between  the  blood 
and  the  tissues.  It  is  here  that  the  tissues  receive  from 
the  blood  the  materials  they  require  for  their  nutrition, 
and  in  the  case  of  glands  for  their  secretion ;  and  it  is 
likewise  here  that  the  blood  receives  from  the  tissues 
their  waste  products.  The  thin  walls  of  the  capillaries 
are  admirably  adapted  for  this  interchange.  In  fact,  it 
is  within  bounds  to  say  that  the  heart,  the  arteries,  and 
the  veins  are  simply  subsidiary  to  the  capillaries,  the 
arteries  carrying  to  these  vessels  the  blood  which  the 
heart  pumps  into  them,  while  the  veins  return  the  blood 
to  the  heart. 

Circulation  in  the  Veins  (Fig.  29). — The  vis  a  tergo  is  not 
exhausted  in  the  capillary  system,  but  is  still  at  work  in 
the  veins,  and  would  of  itself  be  sufficient  to  return  the 
blood  to  the  heart ;  for,  as  has  been  noted,  the  pressure 
in  the  aorta  is  equal  to  a  column  of  mercury  200  mm. 
in  height.  In  the  veins  this  pressure  is  at  most  only 
about  5  mm.,  and  it  is  sometimes  actually  negative,  so 
that  there  is  a  difference  of  pressure  of  195  mm.  of  mer- 


1 88  HUMAN  PHYSIOLOGY. 

cury.  The  vis  a  tergo  is,  however,  in  the  systemic  cir- 
culation— that  is,  that  which  begins  with  the  left  ven- 
tricle and  ends  in  the  right  auricle,  aided  by  two  other 
forces:  i,  compression  of  the  veins;  2,  aspiration  of  the 
thorax. 

Compression  of  the  Veins. — It  will  be  remembered  that 
in  the  veins  there  are,  at  different  points  along  their 
course,  valves  which  are  so  arranged  as  to  permit  the 
blood  to  flow  in  but  one  direction ;  that  is,  toward  the 
heart.  Many  of  these  veins  are  so  situated  with  refer- 
ence to  muscles  that  when  the  muscles  contract  the  con- 
tiguous veins  are  compressed.  This  compression  forces 
the  contained  blood  away  from  the  points  of  pressure, 
and  as  the  closure  of  the  valves  prevents  the  blood  from 
flowing  backward,  it  must  go  forward. 

Aspiration  of  the  Thorax. — At  each  inspiration  the 
cavity  of  the  chest  is  enlarged  and  the  pressure  on  its 
contents  is  diminished.  It  has  already  been  stated  that 
one  of  the  results  of  this  inspiration  is  the  inflowing 
of  air.  Another  result  is  the  inflowing  of  blood  into 
the  venae  cavae  and  right  auricle,  for  while  the  intratho- 
racic pressure  is  diminished,  that  upon  the  blood-vessels 
outside  remains  the  same.  A  similar  tendency  exists  for 
the  blood  in  the  aorta  to  flow  back  into  the  left  ventricle, 
but  this  is  prevented  by  the  aortic  valve.  Inasmuch  as 
the  whole  of  the  pulmonary  circulation  is  within  the 
chest,  all  parts  are  alike  influenced  during  the  respira- 
tory movements,  so  that  the  force  of  aspiration  of  the 
thorax  has  no  effect  upon  this  part  of  the  circulation. 

Fojre  of  Gravity. — The  force  of  gravity  assists  in  the 
return  of  the  blood  to  the  heart  from  the  upper  portions 
of  the  body,  but  retards  its  return  from  the  lower  por- 
tions, so  that  as  a  factor  in  aiding  the  circulation  as  a 


LYMPHATIC  SYSTEM.  1 89 

whole  it  may  be  ignored.  This  force  may,  however,  be 
utihzed  whenever  for  any  reason  there  is  congestion  in 
a  part — as,  for  instance,  in  a  foot  the  seat  of  inflamma- 
tion. In  such  a  case  the  elevation  of  the  lower  extrem- 
ity facilitates  the  flow  of  blood  in  the  veins  and  proves 
beneficial.  Also,  when  by  reason  of  an  imperfect  per- 
formance of  its  function  the  heart  fails  to  send  enough 
blood  to  the  brain,  and  fainting  occurs,  relief  will  come 
more  promptly  if  the  patient  be  at  once  placed  on  the 
back,  with  the  head  lower  than  the  heart,  thus  assisting 
that  organ  in  sending  blood  to  the  anaemic  brain. 

The  average  rate  of  flow  in  the  large  veins  is  about 
100  mm.  per  second.  It  is  slowest  in  the  small  veins, 
and  increases  as  the  heart  is  approached.  The  length 
of  time  required  to  complete  the  entire  systemic  circula- 
tion is  about  twenty-four  seconds.  It  is  estimated  that 
the  blood  occupies  but  one  second  in  traversing  the 
capillaries. 

6.  Lymphatic  System. 

The  lymphatic  system  is  composed  of  lymphatic  ves- 
sels and  lymphatic  glands. 

Lymphatic  Vessels. — The  larger  lymphatic  vessels 
structurally  are  like  the  veins,  being  composed  of  three 
coats,  the  middle  coat  containing  both  muscular  and 
elastic  fibres.  Unlike  the  veins,  however,  muscular  fibres 
are  found  in  the  external  coat.  The  smaller  vessels  have 
only  a  connective-tissue  coat  lined  with  endothelium. 
In  the  lymphatic  vessels,  as  in  the  veins,  are  valves  open- 
ing toward  the  heart.  The  origin  of  these  vessels  in  the 
ti.ssues,  as  a  rule,  is  by  plexuses  or  by  stomata,  as  in 
serous  membranes,  or  by  blind  extremities,  as  in  the 
lacteals.     They   ultimately    discharge    into    the    venous 


190 


HUMAN  PHYSIOLOGY. 


system — on  the  left  side  through  the  thoracic  duct,  and 
on  the  right  side  by  the  right  lymphatic  duct. 


Fig.  30. — Diagram  of  a  Lymphatic  Gland  (Sharpey),  showing  afferent  {fl.l.)  and  effer- 
ent {e.l.)  lymphatic  vessels  ;  cortical  substance  (C) ;  medullary  substance  (71:/)  ;  fibrous 
coat  (c),  sending  trabecule  (tr')  into  the  substance  of  the  gland,  where  they  branch, 
and  in  the  medullary  part  form  a  reticulum  ;  the  trabeculae  are  surrounded  by  the 
lymph-path  or  sinus  (J.s),  which  separates  them  from  the  adenoid  tissue  {l.h). 


Lymphatic  Glands. — The  lymphatic  glands  (Fig.  30)  are 
bodies  of  a  pale  reddish  color,  and  are  oval  in  shape.  Their 
diameter  is  from  2  mm.  to  20  mm.  Lymphatic  vessels 
run  into  the  glands — the  afferent;  and  out  of  them — 
the  efferent;  and  through  them  pass  the  lymph  and  the 
chyle.  They  consist  of  capsule,  trabeculae,  and  alveoli. 
In  the  alveoli  is  the  lymphoid  tissue  containing  the 
lymph-corpuscles   or    leucocytes.     In   passing    through 


DUCTLESS    GLANDS.  I9I 

these  glands  poisonous  matter  which  has  been  absorbed 
by  the  lymph  may  be  deposited,  and  thus  its  entrance 
into  the  blood  may  be  prevented. 

The  lymph  and  its  source,  having  already  been  dis- 
cussed, need  not  again  be  referred  to.  It  is  taken  up  by 
the  lymphatic  capillaries  in  the  tissues  by  endosmosis, 
and,  as  it  accumulates  there,  gradually  fills  the  larger 
vessels,  and,  as  it  is  readily  discharged  into  the  venous 
system,  there  is  set  up  a  current  which  is  the  lymphatic 
circulation.  It  is  to  be  noted,  however,  that  there  is  no 
true  circulation,  as  in  the  case  of  the  blood.  The  blood 
goes  out  from  the  heart  and  returns  again,  completing 
a  circuit,  but  here  the  flow  is  always  in  one  direction, 
toward  the  heart. 

Additional  aids  to  the  endosmotic  force  in  producing 
the  movement  of  the  lymph  are  the  contractions  of  the 
muscles  of  the  body,  by  which,  as  in  the  veins,  the  lym- 
phatics are  compressed,  and  the  lymph,  being  prevented 
by  the  valves  from  flowing  back,  is  propelled  toward  the 
heart.  The  pressure  exerted  by  the  walls  of  the  aorta 
in  its  pulsations  compresses  the  thoracic  duct  in  a  similar 
manner,  and,  as  this  possesses  valves,  the  onflow  of  the 
lymph  and  chyle  is  favored.  The  force  of  aspiration  of 
the  thorax  is  also  a  factor  in  the  movement  of  the  lymph, 
acting  as  was  stated  in  the  case  of  the  venous  blood. 
It  has  been  estimated  that  the  amount  of  lymph  absorbed 
daily  in  a  human  adult  is  about  2000  grammes,  and  of 
lymph  and  chyle  together  3000  grammes. 

7.  Ductless  Glands. 

This  term  includes  the  spleen,  the  thymus  and  thyroid 
glands,  the  suprarenal  capsules,  the  pineal  gland,  and  the 
pituitary  body.     They  have  received  this  name  because 


192  HUMAN  PHYSIOLOGY. 

they  lack  excretory  ducts.  For  the  reason  that  they  are 
beheved  to  have  important  relations  to  the  blood  they 
are  sometimes  described  as  "  blood-glands  "  or  "  vascu- 
lar glands." 

Spleen. — The  weight  of  the  spleen  varies  at  different 
periods  of  life,  being  at  birth  to  the  entire  body  as  i  is 
to  350;  in  adult  life,  as  i  to  320  and  400;  and  in  old 
age,  as  i  to  700,  while  in  certain  diseased  conditions, 
such  as  ague,  syphilis,  or  heart  disease,  it  may  be 
enormously  increased,  in  some  cases  as  much  as  i  to 
7  or  9  kilogrammes,  the  average  normal  weight  being 
about  170  grammes.  The  size  of  the  spleen  is  greatest 
during  digestion  and  least  during  starvation.  The 
splenic  substance  is  made  up  of  fibrous  bands  or  tra- 
beculae,  vessels,  nerves,  Malpighian  bodies,  and  a  dark- 
brown  soft  mass  called  the  "  spleen-pulp."  In  the  latter 
are  cells  and  free  nuclei,  together  with  blood-corpuscles 
both  white  and  red,  many  of  the  red  corpuscles  being  in 
various  stages  of  disintegration.  The  large  size  of  the 
splenic  artery  and  its  tortuosity  are  noteworthy. 

Functions  of  the  Spleen. — The  large  size  of  the  splenic 
artery  suggests  that  under  some  circumstances  a  very 
considerable  amount  of  blood  may  be  carried  to  this 
organ.  This  has  suggested  the  view  that  the  spleen 
might  serve  as  a  reservoir  for  the  blood  when  it  was  not 
needed  in  the  other  abdominal  organs.  This  view  may 
or  may  not  be  correct,  but  this  function  is  certainly  not 
essential,  as  is  shown  by  the  fact  that  after  the  removal 
of  the  spleen,  so  far  as  can  be  seen,  no  interference  with 
the  functions  of  these  organs  occurs. 

Authorities  are  in  general  united  in  the  behef  that  the 
connection  of  the  spleen  with  the  blood  is  intimate. 
Some  of  them  incline  to  the  theory  that  the  red  corpus- 


DUCTLESS   GLANDS.  1 93 

cles  are  here  formed  from  the  white ;  other  authorities 
maintain  that  here  the  red  corpuscles  undergo  disintegra- 
tion ;  while  still  others  attribute  to  the  spleen  the  formation 
of  leucocytes.  This  last  it  certainly  does  to  a  very  great 
extent  in  cases  of  leukaemia. 

Whatever  its  functions  may  be — for  it  is  possible  that 
they  may  be  several — this  organ  is  one  which  is  not 
essential  to  life  either  in  animals  or  in  man.  From  the  dog 
it  has  repeatedly  been  removed,  and  the  results  have  been 
an  increase  of  appetite  and  of  ferocity,  although  in  some 
instances  even  this  was  not  observed.  Besides  these 
changes  the  red  corpuscles  are  diminished  and  the  white 
corpuscles  are  increased,  but,  as  has  already  been  stated, 
the  marrow  of  bones  has  blood-making  powers,  and  this 
marrow  probably  soon  takes  up  the  work  formerly  per- 
formed by  the  spleen  in  making  red  corpuscles,  and  the 
normal  proportions  are  soon  reproduced. 

The  congenital  absence  of  the  spleen  has  occurred  in 
the  human  subject  without  the  corresponding  loss  of 
any  functions  of  the  body  so  far  as  known.  The  human 
spleen  has  also  been  removed,  with  the  result  of  lessen- 
ing the  number  of  red,  and  increasing  the  white,  cor- 
puscles, but  this,  as  in  the  dog,  has  not  been  permanent. 
The  spleen  has  been  extirpated  after  injuries,  and  also 
in  the  condition  known  as  "  floating  spleen  "  and  in  en- 
largement of  the  organ,  but  the  fatal  results  which  have 
followed  have  caused  the  practice  to  be  abandoned. 

Thymus  Gland. — This  organ  belongs  to  foetal  life  and 
to  that  of  early  childhood,  forming  at  the  third  month 
of  intra-uterine  life  and  reaching  its  maximum  of  growth 
at  the  end  of  the  second  year,  at  which  time  it  dimin- 
ishes, and  disappears  at  puberty.  It  is  regarded  by  some 
as  a  producer  of  red  blood-corpuscles,  while  others  con- 

13 


194  HUMAN  PHYSIOLOGY. 

sider  it  a  former  of  leucocytes,  pointing  in  confirmation 
of  this  to  the  fact  that  in  reptiles,  where  lymphatic 
glands  are  not  found,  the  thymus  does  not  atrophy, 
but  is  a  permanent  organ. 

Thyroid  Gland. — The  function  of  the  thyroid  gland  is 
unknown,  although  it  is  regarded  by  some  authorities  as 
a  blood-forming  gland.  The  effect  of  its  removal  would 
seem  to  indicate  that  it  has  something  to  do  with  regu- 
lating the  amount  of  mucin  formed  in  the  body.  After 
this  operation  a  condition  known  as  "  myxoedema "  is 
observed,  in  which  the  connective  tissues  become  infil- 
trated with  a  mucin-containing  material.  A  similar  con- 
dition may  result  from  disease  of  the  thyroid.  Another 
result  of  the  removal  of  the  thyroid  is  cretinism,  a  dis- 
ease common  in  the  Alps,  in  which  there  is  a  condition 
of  the  intellectual  faculties  approaching  idiocy.  Asso- 
ciated with  it,  in  the  Alps,  there  is  usually  goitre,  an  en- 
largement of  the  thyroid.  Goitre  may,  however,  exist 
without  cretinism. 

Suprarenal  Capsides. — The  fact  that  in  some  cases  of 
Addison's  disease  (characterized  by  a  bronzing  of  the 
skin)  the  suprarenal  capsules  have  been  found  diseased 
has  led  some  authors  to  entertain  the  opinion  that  they 
were  in  some  way  related  to  the  coloration  of  the  skin. 
Some  authorities  think  that  they  are  concerned  in  prevent- 
ing the  production  of  too  much  blood-coloring  substance, 
but  as  a  matter  of  fact  nothing  definite  is  known  about 
them.  They  may  be  removed  without  producing  any 
marked  results. 

Pittdtary  Body  and  Pineal  Gland. — These  small  bodies 
are  situated  at  the  base  of  the  brain.  Their  functions 
are  unknown,  but,  being  vascular,  they  are  regarded  as 
belonging  to  the  vascular  ductless  glands. 


THE  SKIN. 


8.  The   Skin. 


195 


The  skin  is  composed  of  a  deep  portion,  the  corium, 
derma,  or  true  skin,  and  of  a  superficial  portion,  the  epi- 
dermis or  cuticle. 

Corium. — The  corium  makes  up  by  far  the  greater  part 


Fig.  31.— Vertical  Section  of  the  Skin,  diagrammatic  (after  Heitzmann). 

of  the  skin,  and  within  it  are  the  perspiratory  glands,  the 
sebaceous  glands,  the  hairs,  together  with  both   blood- 


196 


HUMAN  PHYSIOLOGY. 


and  lymphatic  vessels.  The  upper  surface,  where  it 
joins  the  epidermis,  is  irregular,  being  composed  of 

elevations — papillae — and  in- 
tervening depressions.  In 
some  of  these  papillae  are  the 
tactile  corpuscles,  in  which 
nerve-fibres  end. 

Epidermis. — The  epidermis 
is  made  up  of  a  deep  and  a 
superficial  layer.  The  deep 
layer  (rete  mucosum  or  rete 
Malpighii)  covers  the  papillae 
of  the  corium  and  fills  the 
depressions  between  them. 
It  is  composed  of  cells,  round 
or  of  different  shapes  due  to 
pressure  of  contiguous  cells, 
the  material  of  which  they 
are  composed  yielding  read- 
ily. It  is  in  this  layer  that 
the  pigment  is  deposited 
which  characterizes  the  dark 
Fig.  32.— <:,  corneous  (horny)  layer;  g,  raccs.     The  Superficial  layer 

granular  layer;  wz,  mucous  layer  (rete  ....                                , 

Malpighii).  The  stratum  lucidum  is  the  of  thC  CpidcrmiS  IS  COmpOSed 

layer    just   above   the   granular  layer,  ^f    ^^\\^    which     are     flat    and 

Nerve-terminations  :  n,  afferent  nerve  ; 

^,  terminal  nerve-bulbs  ;/,  cell  of  Lan-  dry    Or    homy, 

gerhaus  (after  Ranvier).  PeVSpirUtOry  Glands.—T\\& 

perspiratory  glands,  also  described  as  sweat-  and  sudo- 
riparous glands,  are  very  numerous,  it  being  estimated 
that  in  the  entire  skin  there  are  not  less  than  2,400,000. 
They  are  more  abundant  in  some  parts  of  the  body  than 
in  others :  in  the  palm  of  the  hand  there  are  42  to  the 
square  centimetre;  on   the   forehead,   190;  and   on  the 


THE  SKIN. 


197 


cheek,  85.  If  all  these  glands  in  the  body  were  straight- 
ened out  and  put  end  to  end,  they  would  extend  a  dis- 
tance of  4  kilometres. 


('. 


I 


Fig.  33. —  C,  epidermis;  /?,  coriiim  ;  /^.papilla;;  .S',  sweat-gland  duct;  »,  arterial  and 
venous  capillaries  (superficial  or  papillary  plexus)  of  the  papillae  (deep  plexus  is 
partly  shown  at  lower  margin  of  the  diagram);  vs,  an  intermediate  plexus,  an  out- 
growth from  the  deep  plexusf.supplying  sweat-glands  and  giving  a  loop  to  hair-papilla 
(after  Ranvier). 

This    brief  consideration   of  the  perspiratory    glands 
suggests  that  their    functi(^n    must    be   very   important. 


198 


HUMAN  PHYSIOLOGY. 


They  are  constantly  at  work  pouring  out  their  secre- 
tions upon  the  surface  of  the  skin.  Ordinarily  this  se- 
cretion is  not  perceptible, 
and  it  is  then  called  "  in- 
sensible perspiration." 
Upon  active  exercise  or 
when  the  temperature  of 
the  air  is  high  this  secre- 
tion becomes  visible,  and 
it  is  then  called  "  sweat  " 
or  "perspiration."  The 
average  total  amount 
daily  formed  is  900 
grammes.  This  amount 
is  subject  to  consider- 
able variations,  being  in- 
creased in  summer  and 
diminished  in  winter. 
During  violent  exercise 
the  amount  may  be  as 
much  as  380  grammes 
per  hour,  and  during  ex- 
posure to  very  high  temperatures  it  has  been  known  to 
reach   18 14  grammes  in  the  same  time. 

The  following  table  shows  the  composition  of  sweat : 

Water    . 99.00  per  cent. 

Urea 15    "      " 

Neutral  fats,  fatty  acids,  choles- 
terin,  sodium  and  potassium 
chloride  and  other  salts  .    .         .85     "      " 

100.00 
Sweat  has  a  salty  taste,  a  specific  gravity  of  1003  to 
1005,  and  is  acid  in  reaction.     It  is  claimed  by  some 


Fig.  34. — A  Normal  Sweat-gland,  highly  mag- 
nified (after  Neumann)  :  a,  sweat-coil,  with 
secreting  epithelial  cells;  b,  sweat-duct;  c, 
lumen  of  duct;  d,  connective-tissue  capsule; 
e  and  f,  arterial  trunk  and  capillaries  sup- 
plying the  gland. 


THE  SKIN. 


199 


writers  that  its  true  reaction  is  alkaline,  and  that  its 
acidity  is  in  reality  due  to  the  presence  of  fatty  acids 
resulting  from  the  decomposition  of  the  sebum.  In 
uraemia  the  amount  of  urea  may  be  so  great  as  to  crys- 
tallize on  the  skin ;  in  dia- 
betes sugar  may  be  found  in 
the  sweat ;  and  in  cases  of 
gout  uric  acid  has  been  de- 
tected. 

Office  of  Perspiration. — One 
of  the  important  means  of 
regulating  the  temperature 
of  the  body  is  the  perspira- 
tion. Without  it  exposure  to 
high  temperatures  would  be 
injurious,  and  in  some  cases 
would  even  be  fatal.  An  ex- 
ternal temperature  of  52°  C. 
is  not  infrequently  met  with 
in  the  southern  part  of  the 
United  States :  to  this  heat 
human  beings  are  exposed 
without  suffering  from  its  ef- 
fects. The  evaporation  of  the 
perspiration  abstracts  heat 
from  the  body.  Of  the  heat 
given  off  from  the  body,  88 
per  cent,  passes  off  by  the 
skin  ;  of  this  amount,  73  per 
cent,  is  by  radiation  and  conduction,  and  14.5  per  cent, 
by  evaporation. 

Sebaceous  Gla?tds. — The    sebaceous  glands  are  race- 
mo.sc  glands,  and  discharge  their  product — sebum — into 


Fig.  35. — A  Normal  Sebaceous  Gland  in 
connection  with  a  lanugo  hair;  greatly 
magnified  (after  Neumann):  a,  con- 
nective-tissue capsule ;  b,  fatty  secre- 
tion; c,  h,  fat-secreting  cells;  d,  root 
of  a  lanugo  hair;  e,  hair-sac;  /,  hair- 
shaft;  g,  acini  of  sebaceous  gland. 


200  HUMAN  PHYSIOLOGY. 

the  hair-follicles  of  large  hairs,  as  upon  the  scalp,  while 
in  other  portions  of  the  body,  as  the  forehead,  where  the 
hairs  are  small,  the  hair  projects  from  the  mouth  of  the 
sebaceous  gland,  and  is  more  like  an  appendage  than  a 
separate  structure. 

Composition  of  Sebum. — The  sebum,  or  sebaceous 
matter,  is  of  an  oily  nature.  It  contains  albumin,  fat,  and 
cholesterin.  The  vernix  caseosa  which  covers  the  infant 
during  the  latter  part  of  foetal  life  is  of  the  same  charac- 
ter, consisting  principally  of  fat  with  epithelium.  At  the 
temperature  of  the  body  the  sebum  is  fluid,  but  it  solid- 
ifies on  the  surface  of  the  skin.  Its  office  is  mainly  to 
keep  the  skin  and  the  hairs  soft  and  pliable.  Besides 
this  it  is  probably  excrementitious  to  a  certain  extent. 

Cernuicn,  commonly  called  "  ear-wax,"  is  the  product 
of  the  sebaceous  and  perspiratory  glands  of  the  external 
auditory  meatus,  and  is  composed  principally  of  fat  with 
some  soap.  It  is  a  reddish  substance  having  a  sweetish- 
bitter  taste. 

Hairs  and  Nails. — These  structures  are  modified 
epidermis.  The  hair  grows  from  the  hair-papilla,  in 
the  interior  of  which  there  is  a  blood-vessel.  The  in- 
tegrity of  this  papilla  is  essential  to  the  existence  of  the 
hair ;  when  destroyed  the  hair  can  never  be  reproduced. 
It  should  be  noted  that  the  hair-papillae  and  the  papillae 
already  described  in  connection  with  the  corium  are 
very  different  structures,  and  they  should  not  be  con- 
founded. It  has  been  estimated  that  there  are,  on  an 
average,  120,000  hairs  in  the  scalp.  As  a  rule,  the 
lighter  the  color  of  hair  the  finer  it  is ;  in  the  female  it 
is  coarser  than  in  the  male. 

Functions  of  the  Skin. — The  functions  of  the  skin  are 
numerous  and  very  important. 


THE  SKIN. 


201 


(i)  Protection. — The  tissues  which  He  beneath  the  skin 
are  delicate  and  sensitive,  and  are  protected  from  injury 
by  it.     The  epidermis,  by  reason  of  its  hard  and  tough 


Fig.  36. — A,  shaft  of  the  hair ;  B,  root  of  the  hair  ;  C,  cuticle  of  the  hair;  D,  medul- 
lary suhstance  of  the  hair  ;  K,  external  layer  of  the  hair-follicle  :  F,  middle  layer 
of  the  hair-follicle:  G,  internal  layer  of  the  hair-follicle  ;  H,  papilla  of  the  hair ;  I, 
external  root-sheath  ;  J,  outer  layer  of  the  internal  root-sheath  ;  K,  internal  layer  of 
the  internal  root-sheath  (after  Duhring). 

character,  especially  in  the  palms  of  the  hands  and  on 
the  soles  of  the  feet,  is  peculiarly  adapted  to  this  end. 

(2)  Excretion. — It  has  already  been  noted  that  by  the 
skin  a  litre  of  fluid  is  daily  eliminated  from  the  body. 
In  this  fluid  are  dissolved  materials  representing  the 
waste  of  the  tissues.  There  is  a  reciprocal  relation 
between  the   skin   and   the  kidneys  :   in   summer,  when 


202 


HUMAN  PHYSIOLOGY. 


the  skin  is  active,  the  amount  of  fluid  passed  off  by  the' 
kidneys  is  reduced,  while  in  winter,  when  the  skin  is 
inactive,  the  work  of  the  kidneys  is  much  increased.  In 
diseased  conditions  of  the  kidneys,  when  these  organs 
are  incapacitated  for  the  performance  of  their  function, 
the  retention  in  the  blood  of  poisonous  materials  which 
are  eliminated  in  health  is  prevented  by  causing  the  per- 
spiratory glands  of  the  skin  to  assume  the  task. 


Fig.  37.— a,  a  vascular  papilla ;  b,  a  nervous  papilla  ;  c,  a  blood-vessel ;  d,  a  nerve- 
fibre;  e,  a  tactile  corpuscle  (after  Biesiadecki). 

(3)  Sensation.— T\\&  skin,  especially  at  the  tips  of  the 
fingers,  being  very  sensitive,  gives  knowledge  of  the  con- 
sistency of  objects,  whether  they  are  rough  or  smooth, 
sharp  or  dull,  hard  or  soft,  etc.  This  subject  of  general 
sensibility  will  be  fully  discussed  in  connection  with  the 
Nervous  Functions. 


THE  SKIN.  203 

(4)  Respiration. — Interchanges  are  constantly  taking 
place  in  the  skin  analogous  to  those  which  take  place  in 
the  lungs,  although  to  a  much  less  extent.  Oxygen  is 
absorbed  from  the  air  by  the  blood  in  the  cutaneous 
blood-vessels,  and  at  the  same  time  carbon  dioxide  is 
given  off.  In  frogs  these  interchanges  are  much  more 
extensive  than  in  man. 

(5)  Regulation  of  temperature,  which  has  already 
been  discussed. 

Care  of  the  Skin. — That  the  skin  may  perform  its  func- 
tions properly  it  must  be  taken  care  of.  The  orifices  of 
the  ducts  of  the  perspiratory  and  sebaceous  glands  must 
be  kept  free,  so  that  they  may  not  become  clogged.  If 
the  skin  of  an  animal  be  covered  with  varnish,  it  speedily 
dies.  This  is  not  due  to  the  retention  of  waste  materials, 
which  act  as  poisons,  but  to  the  great  loss  of  heat,  in 
the  rabbit  the  temperature  falling  to  20°  C.  Experiment 
has  shown  that  if  an  animal  that  has  been  varnished  be 
packed  in  cotton  and  kept  in  a  temperature  of  30°  C,  it 
will  survive. 

The  skin  requires  both  friction  and  bathing  to  main- 
tain it  in  a  physiological  condition.  The  process  of  rub- 
bing removes  the  useless  epidermic  scales  and  any  ob- 
structions which  tend  to  clog  the  mouths  of  the  glands. 
The  oily  nature  of  the  sebaceous  matter,  which  is  always 
present  and  which  retains  the  dust  and  dirt  coming  in 
contact  with  it,  requires  that  the  skin  be  washed  with 
water  and  soap.  But  the  soap  must  be  free  from  irritat- 
ing ingredients,  such  as  rancid  fat,  and  from  too  large  an 
amount  of  alkali  and  coloring  matter,  and  from  drugs  of 
various  kinds.  If  the  skin  be  diseased,  medication  by 
means  of  soap  maybe  needed,  but  it  should  be  prescribed 
by  a  physician.     If  the  skin  be  not  diseased,  medicated 


204  HUMAN  PHYSIOLOGY. 

soaps  are  harmful.  Old  white  castile  soap  meets  all  the 
indications  in  health. 

Baths. — Baths  may  be  classified  as  follows  : 

Cold  bath o°  to  24°  C. 

Temperate  bath 24°  to  26°  C. 

Tepid  bath 26°  to  32°  C. 

Warm    " 32°  to  37°  C. 

Hot        "      . 37°  to  44°  C. 

As  a  rule,  hot  baths  are  relaxing,  and  should  not,  there- 
fore, be  indulged  in  too  frequently ;  indeed,  in  persons 
suffering  with  disease  of  the  heart  they  may  actually 
endanger  life.  The  Turkish  bath,  taken  under  compe- 
tent medical  supervision,  is  often  of  great  benefit,  and 
many  persons  take  it  weekly,  and  even  oftener,  with  the 
effect  of  toning  up  the  system  and  of  making  them  more 
competent  to  endure  both  physical  and  mental  fatigue. 
Cold  baths,  except  for  the  very  robust,  are  also  to  be 
taken  with  great  caution.  If  afterward  there  be  reaction 
and  if  the  skin  become  warm  and  pink,  they  are  bene- 
ficial, but  if  the  skin  become  cold  and  blue,  they  are 
injurious.  In  fact,  this  should  be  the  test  for  each  indi- 
vidual to  apply  to  his  own  case.  Bathing,  except  a 
sponge-  or  plunge-bath,  should  not  be  practised  when  the 
vital  powers  are  low,  as  early  in  the  morning,  nor  after 
a  long  fast,  nor  should  it  be  indulged  in  too  soon  after 
eating;  eleven  o'clock  in  the  morning  is,  for  the  average 
person,  a  proper  time  for  a  bath  of  considerable  duration. 


9.  Kidneys. 

The   kidneys  are   situated  in  the  lumbar  region   of 
the  abdominal   cavity,  one  on  each  side  of  the  spinal 


PLATE     III. 


A,  A,  right  atul  left  kidneys  ;    B,  urinary  Ijladdcr  ;    C.  C.  ii«ht    and    lufl   ureters;    d,  d, 
renal  arteries. 


KIDNE  YS. 


205 


column.  The  shape  of  the  kidney  is  like  that  of  a  bean, 
the  internal  border  being  concave  and  presenting  a 
fissure — the    hilum — at    which   the  vessels,   the   nerves, 

When  the  kidney  is 


and  the  ureter  enter  the  organ 


Fig.  38. — Longitudinal  Section  through  the  Kidney  (after  Tyson  and  Henle)  :  i,  cor- 
tex ;  i',  medullary  rays  ;  i",  labyrinth  ;  ■z,  medulla  ;  2',  papillary  portion  of  medulla; 
2",  boundary  layer  of  medulla  ;  3,  transverse  section  of  tubules  in  the  boundary 
layer;  4,  fat  of  renal  sinus  ;  5,  artery  ;  *,  transverse  medullary  rays  ;  A,  branch  of 
renal  artery  ;   C,  renal  calyx  ;    U,  ureter. 

longitudinally  cut  in  two,  it  is  seen  to  be  made  up  of  an 
external  or  cortical  portion — cortex — and  an  internal  or 
medullary  portion.     The  medullary  portion  is  made  up 


2o6 


HUMAN  PHYSIOLOGY. 


of  numerous  pyramids  (those  of  Malpighi),  from  eight  to 
eighteen  in  number,  and,  dipping  down  between  them, 

as   well   as    forming    the 

I  outer  part  of  the  kidney, 
is  the  cortical  portion. 
Each  pyramid  terminates 
in  a  papilla  projecting  into 
a  calyx,  which,  with  the 
calices  of  other  pyramids, 
forms  the  pelvis,  the  upper 
dilated  cavity  of  the  ureter. 
At  each  papilla  there 
open  about  twenty  urinif- 
erous  tubules,  which  can 
be  traced  to  the  base  of 
the  pyramid.  Each  tubule 
continues  into  the  cortical 
portion  of  the  kidney, 
where  it  is  larger  and  be- 
comes convoluted,  nar- 
rowing again  and  entering 

Fig.  39.— Diagram  of  Two  Uriniferous  Tu-     the    pyramid,    in    which     it 
bules  (Tyson  and  Brunton,  after  Klein  and  •  1  i.       •     i  i. 

isj -,    ,:  .,, ,       1-,  ,  .  , .     ,  f,     ,    agam    becomes     straight, 

JNoble    smith):    i,    Malpighian   tuft    sur-        fc>  o       ' 

rounded  by  Bowman's  capsule;  2,  con-  fomiS  a  loOp,  and  rC-entCrS 
striclion,  or  neck  ;  3,  proximal  convoluted 
tubule;  4,  spiral  tubule;  5,  descending 
limb  of  Henle's  loop;  6,  Henle's  loop; 
7  and  8,  ascending  limb  of  Henle's  loop ; 
9,  wavy  part  of  ascending  limb  of  Henle's 
loop;  10,  irregular  tubule;  11,  distal  con- 
voluted tubule;  12,  first  part  of  collecting 
tube;  13  and  14,  straight  part  of  collecting  pighiaU  CapSule  Or  Cap- 
tube;  15,  excretory  duct  of  Bellini.  g^j^    ^^   BoWmaU. 

This  complicated  structure  may,  perhaps,  be  traced 
more  easily  in  the  opposite  direction.  Beginning  with 
the  Malpighian  capsule  in  the  cortical  portion,  there  is 


the  cortical  portion,  again 
becomes  convoluted,  and 
finally  terminates  in  a 
spherical  body,  the   Mai- 


KIDNE  YS. 


207 


next  the  convoluted  tubule,  which,  as  it  passes  into  the 
medullary  portion,  becomes  straight  and  is  known  as  the 
"descending  limb  of  Henle's  loop."  This  bends  on  itself, 
forming  the  ascending  limb,  likewise  straight,  passes  back 
into  the  cortex,  becomes  convoluted,  and  enters  a  straight 
collecting  tube  which  opens  at  the  apex  of  a  pyramid. 

The  Malpighian  capsule  is  lined  by  a  layer  of  squa- 
mous epithelium  which  is  reflected  over  the  glomerulus 
it  contains.  Between  these  two  layers  of  cells  there  is  a 
cavity  continuous  with  the  uriniferous  tubule.  The  tubule 
throughout  its  entire  length  is  lined  by  epithelium,  which, 
however,  varies  in  character  in  different  portions. 

The  renal  artery  enters  the 
kidney  at  its  hilum,  and  its 
branches,  after  pursuing  a  pe- 
culiar course,  terminate  in  af- 
ferent vessels,  each  of  which 
penetrates  the  wall  of  a  Mal- 
pighian capsule,  forming  the 
glomerulus.  The  vessels  com- 
ing from  the  capsules — efferent 
vessels — pass  out  through  their 
walls  and  form  a  venous  plexus 
around  the  uriniferous  tubules, 
ultimately  taking  part  in  the 
formation  of  the  renal  vein, 
which  emerges  from  the  kidney 
at  the  hilum  and  discharges 
into  the  inferior  vena  cava. 

Urine. — The  function  of  the  kidney  is  to  form  the  urine, 
which  is  a  yellow  or  amber-colored  fluid,  acid  in  reaction, 
and  having  a  specific  gravity  of  about  1020  in  the  adult ; 
in  the  new-born  child,  of  about  1005.     The  quantity  of 


Fig.  40.— Bowman's  Capsule  and 
Glomerulus  (after  Landois)  :  a,  vas 
afferens  ;  e,  vas  efferens  ;  c,  capil- 
lary network  of  the  cortex;  k,  en- 
dothelial structure  of  the  capsule; 
h,  origin  of  convoluted  tubule. 


208 


HUMAN  PHYSIOLOGY. 


urine  voided  in  twenty-four  hours  is  about  1 500  grammes. 
Water  constitutes  95.2  per  cent,  and  the  solids  4.8  per 
cent.,  of  which  2.2  per  cent.,  nearly  one-half,  is  urea. 
The  following  table  shows  the  composition  of  urine : 


Percentages. 

96.0 

2.0 

•OS 
.04 
.II 


1-5 


Daily  amount. 

1450.  grammes. 
30. 

0.75  " 

0.75  " 

1.5  " 

3-  " 

7-5  " 

3.  " 


Water  .... 
Urea     .... 
Uric  acid     .    . 
Hippuric  acid 
Creatinin     .    . 
Phosphates  ^ 
Chlorides      > 
Sulphates    J 
Mucus  and  other  in- 
gredients      3 

The  general  characteristics  of  the  urine  and  its  com- 
position are  subject  to  considerable  variation  in  a  condi- 
tion of  health.  It  may,  when  its  specific  gravity  is  low 
(1002),  be  almost  colorless,  while  when  concentrated  its 
color  will  be  a  reddish-brown.  Its  reaction,  although 
generally  acid,  may  be  alkaline,  as  at  the  beginning  of 
digestion,  or  its  acidity  may  be  increased,  as  during  the 
afternoon  or  the  night.  The  kind  of  food  also  affects 
the  reaction.  Thus  in  the  carnivora  the  urine  is  acid, 
while  in  the  herbivora  it  is  alkaline.  If  vegetables  be 
fed  to  a  carnivorous  animal  and  flesh  to  an  herbivorous, 
the  reaction  of  the  urine  will  be  the  opposite  to  that  of 
the  urine  when  each  is  consuming  its  normal  food  The 
feeding  of  flesh  to  the  herbivorous  animal  is  practically 
accomplished  by  giving  it  no  food,  under  which  circum- 
stances it  lives  upon  its  own  tissues.  The  acidity  of 
urine  is  usually  attributed  to  acid   sodium  phosphate, 


KIDNE  YS.  209 

but  several  organic  acids  or  organic  salts  are  probably 
involved.* 

Water. — The  amount  of  water  excreted  daily  is  on  an 
average  1450  grammes,  and  constitutes  96  per  cent,  of 
the  urine.  It  is  separated  from  the  blood  by  the  epi- 
thelial cells  covering  the  glomerulus,  and  not  by  fil- 
tration due  to  blood-pressure.  It  is  true  that  as  blood- 
pressure  in  the  glomerulus  increases  the  amount  of  water 
eliminated  also  increases,  but  this  is  not  due  to  the  sim- 
ple increase  of  pressure,  but  is  due  to  the  fact  that  with 
increased  pressure  more  blood  flows  through  the  glom- 
erulus ;  consequently  there  is  more  material  from  which 
the  cells  can  separate  water. 

Urea. — Of  all  the  ingredients  of  the  urine,  urea  is  the 
most  important.  It  represents  to  a  great  extent  the 
nitrogenous  waste  of  the  tissues.  The  amount  of  urea 
daily  excreted  is  in  the  male  about  30  grammes ;  it  is 
less  in  the  female.  The  actual  amount  eliminated  in 
children  is  less,  but,  proportional  to  the  weight  of  the 
body,  the  child  excretes  more  urea  than  does  the  adult. 

Source  of  Urea. — The  ingredient  urea  is  not  formed 
by  the  kidney:  it  exists  in  the  blood  when  this  fluid 
reaches  the  kidney,  and  this  organ  separates  it  from  the 
blood.  The  separation  is  brought  about  by  the  epithelium 
of  those  portions  of  the  uriniferous  tubules  about  which 
is  entwined  the  venous  plexus  already  referred  to  ;  that  is, 
the  convoluted  tubules  and  the  ascending  limb  of  Henle's 
loop.  The  source  of  urea  is  threefold:  i,the  proteids  of 
the  food;  2,  the  proteids  of  the  tissues;  and  3,  the  pro- 
teids of  the  blood  and  lymph. 

I .  Urea  from  the  Proteids  of  the  Food. — The  greater 
the  amount  of  proteids  absorbed,  the  greater  is  the 
amount  of  urea  excreted.     Thus  if  large  quantities  of 

H 


2  I O  HUMAN  PHYSIOL  OGY. 

meat  be  eaten,  the  amount  of  urea  in  the  urine  will  be 
very  large,  whereas  if  food  without  nitrogen  in  its  com- 
position be  taken,  the  urea  will  be  present  in  a  minimum 
amount.  It  might  be  thought  that  the  increased  amount 
of  urea  excreted  under  these  circumstances  is  derived  from 
the  tissues,  but  it  appears  in  so  short  a  time  (an  hour  or 
two)  that  this  cannot  be  the  case.  In  discussing  intes- 
tinal digestion  it  was  stated  that  when  an  excess  of  pro- 
teid  food  was  taken  the  overplus  of  the  peptones  was 
changed  into  leucin  and  tyrosin  by  the  action  of  the 
trypsin.  These  two  substan'ces  are  absorbed  by  the 
blood-vessels  and  carried  by  the  portal  vein  to  the  liver, 
where  they  are  probably  converted  into  urea.  There  is 
no  direct  proof  of  this  conversion,  but  the  hypothesis  is  a 
reasonable  one,  for  so  far  as  is  known  the  liver  is  the  only 
gland  which  contains  urea,  and,  further,  it  has  been  shown 
that  when  leucin  is  fed  to  animals  it  reappears  as  urea. 

2.  Urea  from  the  Proteids  of  the  Tissues. — The  muscles 
contain  creatin  to  the  amount  of  from  0.2  to  0.4  per  cent. 
Creatin  is  recognized  as  a  substance  intermediate  between 
proteids  and  urea,  and  it  exists  also  in  the  brain  and  ner- 
vous system  generally,  in  the  spleen,  and  in  various 
glands.  Creatin  in  all  probability  is  one  of  the  sources 
of  urea,  but  where  the  conversion  takes  place  is  un- 
known ;  possibly  it  is  accomplished  by  the  epithelium 
of  the  tubules  of  the  kidney. 

3.  Urea  from  the  Proteids  of  the  Blood  and  Lymph. — 
All  the  proteids  present  in  the  blood  and  lymph  do  not 
become  integral  parts  of  the  tissues,  so  that  there  is  a 
certain  amount  of  the  proteids  constantly  circulating. 
The  circulating  proteids  are  not  permanent,  but,  like 
other  proteids,  undergo  conversion  into  urea.  It  is  not  to 
be  assumed  from  this  statement  of  the  origin  of  urea  that 


KIDNE  YS. 


211 


the  proteids  are  converted  directly  into  that  substance. 
It  has  ah'eady  been  seen  that  there  are  some  intermediate 
stages — for  example,  leucin,  tyrosin,  and  creatin — and 
there  are  doubtless  others  of  which  nothing  is  known. 

Uric  Acid. — Besides  being  an  ingredient  of  the  urine, 
uric  acid  has  also  been  detected  in  the  spleen,  the 
heart,  the  liver,  and  the  brain.  In  the  blood  it  is  also 
present,  especially  in  gout.  In  the  urine  the  amount 
of  uric  acid  under  ordinary  circumstances  does  not 
exceed  0.75  grammes  per  diem.  The  amount  will 
be  still  less  if  the  diet  be  vegetable,  but  if  it  be  ani- 
mal and  abundant  the  quantity  may  be  as  much  as  2 
grammes.  It  is  less  in  attacks  of  gout,  during  which  the 
quantity  in  the  blood  is  increased.  In  febrile  conditions 
the  amount  is  also  increased.  Uric  acid  is  not  free  in 
the  urine,  but  is  combined  with  sodium,  ammonium, 
potassium,  calcium,  and  magnesium  to  form  urates,  the 


Fig.  41. — Uric  Acid  and  Urates  (Fiiiike). 


sodium  and  ammonium  urates  being  the  most  abundant. 
Under  ordinary  circumstances  it  remains  in  combination, 


212  HUMAN  PHYSIOLOGY. 

but  when  the  urine  is  very  acid  it  appears  in  the  form 
of  crystals  (Fig.  41). 

So2irce  of  Uric  Acid. — Uric  acid  is  regarded  by  some 
writers  as  being  an  intermediate  product  in  the  forma- 
tion of  urea.  These  believe  that  the  process  of  oxidation 
of  the  nitrogenous  materials  has  for  some  reason,  as  from 
an  insufficient  supply  of  oxygen,  been  arrested  before  the 
stage  of  urea  is  reached ;  but  this  theory  of  the  formation 
of  uric  acid  has  not  been  substantiated.  From  the  evi- 
dence now  at  our  disposal  it  must  be  regarded  as  one 
of  the  final  products  of  oxidation,  as  is  the  case  with 
urea.  There  is  some  evidence  that  uric  acid  is  formed 
in  the  spleen  of  man,  the  quantity  eliminated  being  in- 
creased when  the  spleen  is  enlarged,  and  being  dimin- 
ished when  this  organ  is  reduced  in  size.  There  is  no 
reliable  evidence  that  the  human  liver  produces  this  acid, 
although  it  is  doubtless  formed  in  the  liver  of  birds. 

Hippiiric  acid,  another  ingredient  of  urine,  is  excreted 
in  about  the  same  amount  as  uric  acid.  A  vegetable 
diet,  especially  of  fruits,  may  increase  this  excretion  to 
2  grammes  daily.  Hippuric  acid  has  also  been  found  in 
perspiration  and  in  blood. 

Creatinin. — As  shown  by  the  table,  creatinin  is  ex- 
creted daily  to  the  amount  of  1.5  grammes.  It  is  con- 
sidered as  being  formed  from  creatin,  and  is  spoken  of 
as  the  anhydride  of  creatin.  Creatin,  it  will  be  remem- 
bered, is  a  constituent  of  muscles  especially,  although  it 
is  found  also  in  nervous  tissue.  As  would  be  expected 
from  its  derivation,  the  quantity  in  urine  will  be  increased 
under  a  diet  of  flesh. 

Inorganic  Constituents  of  Urine. — The  inorganic  con- 
stituents of  urine  are  principally  phosphates,  chlorides, 
and   sulphates.     The  phosphates  especially  worthy  of 


KIDNE  YS. 


213 


mention  are  those  of  sodium,  both  neutral  and  acid.    To 
the   latter   is   attributed  the  acidity  of  the  urine.     The 


Fig.  42. — Calcium  Phosphate  (Laache). 


phosphates  of  the  urine  are  derived  from  the  phosphates 
of  the  food,  and  there  is  no  foundation  for  the  theory  that 


Fig.  43.— Triple  Phosphates  and  Ammonium  Urate  (Laache). 


they  are  increased  by  mental  exertion  and  represent  the 
waste  of  nerve-tissue.     The  amount  of  phosphates  ex- 


214  HUMAN  PHYSIOLOGY. 

creted  is  increased  in  fevers  and  in  diseases  of  the  bones, 
and  is  diminished  during  pregnancy.  The  chlorides 
are  mainly  represented  by  the  chloride  of  sodium,  and, 
as  they  are  derived  from  the  food,  the  amount  eliminated 
depends  upon  the  amount  in  the  food.  In  pneumonia 
the  amount  of  chlorides  is  diminished.  The  sulphates 
in  the  urine  are  principally  salts  of  potassium  and  sodium, 
which  are  derived  from  the  food,  but  they  differ  in  this 
respect  from  the  phosphates  and  chlorides,  that  while 
the  latter  exist  in  the  food  in  the  same  form  as  in  the 
urine,  the  sulphates  are  derived  principally  from  the 
proteids,  of  which  sulphur  is  a  constituent,  while  the 
sulphates  of  the  food  contribute  but  little. 

Coloring-matter  of  the  Urine. — The  coloring-matter  of 
the  urine  is  not  ordinarily  abundant.  It  probably  does 
not  consist  of  one  substance  alone,  but  of  several,  the 
best  known  of  which  is  urobilin.  Some  writers,  how- 
ever, hold  that  normal  urine  contains  but  one  pigment, 
to  which  the  name  "  urochrome  "  has  been  given.  "  Uro- 
erythrin  "  is  the  name  given  to  the  coloring-matter  in 
pink  urinary  deposits  and  to  the  highly- colored  urine 
present  in  rheumatism,  and  "  urinary  melanin  "  to  that 
found  in  the  dark-brown  or  black  urine  of  persons  suf- 
fering from  melanotic  tumors,  the  color  of  which  is  very 
dark,  due  to  the  presence  of  melanin. 

Mucus. — The  urine  contains  mucus,  derived  from  the 
various  passages  through  which  it  passes,  which  under 
normal  conditions  has  no  decomposing  action  on  the 
urea. 

Gases  of  the  Urine. — Oxygen,  nitrogen,  and  carbon 
dioxide  are  present  in  the  urine,  the  latter  gas  being  the 
most  abundant,  the  quantity  being  increased  after  active 
muscular  exertion. 


III.  NERVOUS   FUNCTIONS. 

I.  General  Considerations. 

There  is  a  most  intimate  relationship  existing  be- 
tween the  different  organs  of  the  body — so  intimate, 
indeed,  that  not  one  of  the  whole  number  can  be  said 
to  be  entirely  independent.  Many  illustrations  of  this 
dependency  might  be  given,  but  one  will  suffice. 

The  respirations  of  an  individual  at  rest  are  not  far 
from  sixteen  per  minute,  and  the  pulsations  of  the  radial 
artery  are,  in  the  same  condition,  about  seventy.  If, 
now,  he  exercise  violently — running  around  the  block, 
for  instance — the  respirations  will  be  found  to  have 
greatly  increased,  amounting  perhaps  to.  thirty  per 
minute,  while  at  the  same  time  the  pulsations  of  the 
artery  will  have  reached  one  hundred  and  twenty  per 
minute.  Is  this  change  from  the  quiescent  condition  a 
mere  coincidence,  or  is  there  a  reason  for  it  ?  If  the 
latter,  how  has  the  change  been  brought  about  ? 

During  a  resting  condition  the  muscles  of  the  body 
do  not  make  much  demand  upon  the  blood,  and  with 
the  heart  beating  seventy  times  per  minute  the  muscles, 
as  well  as  the  other  tissues,  are  receiving  all  the  material 
they  need  for  the  performance  of  their  functions.  The 
sixteen  respirations  a  minute  are  also  sufficient  to  supply 
the  blood  with  all  the  oxygen  required  and  to  remove 
from  it  the  necessary  amount  of  carbon  dioxide.  When, 
however,  the  muscles  are  called  upon  for  the  increased 
exertion  above  referred  to,  they  must  have  a  greater  sup- 
ply of  the  necessary  materials,  to  furnish  which  a  larger 
amount  of  blood  must  be  sent  to  them.     Then,  too,  as  a 

215 


2l6  HUMAN  PHYSIOLOGY. 

result  of  the  extra  work,  more  muscular  tissue  is  wasted, 
and  the  waste  must  be  taken  away  rapidly  to  the  organs 
whose  duty  it  is  to  eliminate  it.  To  send  the  larger  sup- 
ply of  blood  the  heart  must  beat  faster,  and  to  provide 
the  increased  oxygen  and  to  remove  the  additional  car- 
bon dioxide  the  respiratory  movements  must  be  more 
rapid.  The  muscles  of  the  body  have  not  the  power 
within  themselves  to  increase  their  activity,  but  when 
acted  upon  properly  from  without  they  have.  Neither 
has  the  heart-muscle  the  power  to  beat  more  quickly 
until  stimulated  thereto  by  some  influence  outside  itself. 
Equally  powerless  are  the  agencies  which  produce  the 
respiratory  movements.  These  outside  influences,  by 
which  the  muscles  contract  and  by  which  the  heart  and 
the  respiratory  apparatus  act  in  harmony,  are  derived 
from  the  nervous  system,  a  collection  of  organs  one  of 
whose  functions  is  to  cause  the  different  organs  to  act 
harmoniously.  The  effect  of  a  want  of  harmony  under  the 
circumstances  just  supposed  would  be  most  disastrous. 
If  the  nervous  force  were  not  at  command  to  make  the 
muscles  respond  when  their  increased  action  was  desired, 
there  would  be  a  condition  of  paralysis,  or  if,  when  the 
muscles  attempted  to  perform  this  added  task,  the  heart 
should  fail  to  respond,  the  effort  would  be  fruitless,  and 
equally  unavailing  would  be  the  attempt  if  at  the  crucial 
moment  the  lungs  and  other  respiratory  organs  should 
be  unresponsive.  As  was  said,  many  illustrations  of  the 
interdependence  of  the  organs  might  be  given,  but  a  little 
reflection  will  suggest  them  almost  ad  infinitum. 

The  simplest  movements  that  are  made  require  for 
their  performance  the  conjoint  action  of  several,  often 
many,  muscles,  and  were  it  not  for  the  exciting  and  con- 
trolling power  of  the  nervous  system,  instead  of  the  har- 


NERVOUS  FUNCTIONS.  21/ 

mony  which   is   everywhere   and  at  all   times   apparent 
there  would  result  the  utmost  confusion. 

In  what  has  been  said  thus  far  reference  has  been  had 
only  to  the  individual,  as  if  he  were  alone  on  the  face  of 
the  earth  and  interested  only  in  himself;  but  there  are 
other  human  beings  with  whom  he  is  constantly  brought 
into  relation,  and  a  world  of  other  animate  objects  as  well 
as  an  infinite  amount  of  inanimate  matter.  This  relation- 
ship is  also  accomplished  through  the  nervous  system, 
principally  by  means  of  the  special  senses.  It  will, 
therefore,  be  seen  that  the  nervous  functions  are  those 
which  bring  the  different  organs  of  the  body  into  har- 
monious relations  with  one  another,  and,  in  addition, 
bring  the  individual,  through  the  special  senses,  sight, 
hearing,  etc.,  into  relation  with  the  world  outside  him. 

The  nervous  system  is  made  up  of  collections  of  nervous 
tissue,  which  is  composed  of  two  kinds  of  matter — cel- 
lular or  vesicular,  and  fibrous. 

Cellular  or  vesicular  nerz'ous  matter  is  found  in  the  ex- 
ternal portions  of  the  brain,  the  internal  portions  of  the 
spinal  cord,  and  in  ganglia  generally,  a  ganglion  being  a 
collection  of  nerve-cells.  Such  a  collection  of  nerve-cells 
is  also  .spoken  of  as  a  "  nerve-centre,"  being  so  called  for 
the  reason  that  it  is  composed  of  nerve-cells  or  vesicles 
(Fig.  44).  From  its  grayish  color  it  is  also  known  as 
gray  nervous  matter,  and,  because  of  its  ashy  appear- 
ance, as  cineritious  nervous  matter.  When  examined 
under  the  microscope  it  is  seen  to  be  made  up  of  nerve- 
cells  or  ganglion-corpuscles,  which  are  the  characteristic 
elements,  together  with  nerve-fibres  and  blood-vessels, 
all  imbedded  in  neuroglia,  a  form  of  connective  tissue. 

Nerve-cells  vary  in  size,  from  10  m.mm.  in  the  sympa- 
thetic ganglia  to  135  m.mm.  in  the  anterior  cornua  of  the 


2l8 


HUMAN  PHYSIOLOGY. 


spinal  cord.  These  bodies  vary  also  somewhat  in  shape, 
some  being  spherical  and  others  ovoid,  while  still  others 
are  exceedingly  angular.  They  possess  very  prominent 
nuclei  and  nucleoli,  and  they  have  processes  varying  in 
number  and  giving  rise  to  a  nomenclature  by  which  they 
are  distinguished.     Cells  with  one  process  or  pole  are 


Fig.  44. — Multipolar  Nerve-cells :  a,  from  the  anterior  gray  column  of  the  spinal  cord 
of  the  dog-fish  Ij'ing  on  a  texture  of  fibrils,  c\  b,  prolongation  from  cells  ;  d,  nerve- 
fibres  cut  across  (Cadiat). 

unipolar ;  with  two  poles,  bipolar ;  with  three  or  more 
poles,  multipolar.  Sometimes  cells  are  found  having  no 
process ;  to  such  the  term  apolar  has  been  given.  It  is 
doubtful,  however,  whether  there  are  such  cells,  except 
as  the  result  of  accident  by  which  a  process  has  been 
broken  off  In  the  spinal  ganglia  unipolar  cells  exist, 
while  in  the  cord  cells  are  found  the  number  of  whose 
processes  is  as  many  as  eight.  Frequently  the  processes 
may  be  seen  to  be  branched,  the  branches  themselves 
subdividing  again  and  again.  Often,  however,  one  pro- 
cess may  be  traced  for  a  considerable  distance  from  the 
nerve-cell    in  which  it   originated  without  any  branch 


NERVOUS  FUNCTIONS. 


219 


being  discovered.  Such  a  process  is  continuous  with 
the  axis-cyHnder  of  a  nerve-fibre,  and  is  therefore  called 
the  "  axis-cylinder  prolonga- 
tion." The  branched  pro- 
cesses disappear  in  the  nerv- 
ous tissue :  they  probably  con- 
nect with  processes  from  other 
nerve-cells. 

Fibrous  nervous  matter, 
which  is  the  material  com- 
posing nerve-fibres,  is  of  two 
kinds  :  (i)  medullated,  and  (2) 
non-medullated. 

{\)  Medullated  fibres,  which 
are  called  also  "  white  fibres  " 
by  reason  of  their  color, 
make  up  the  white  por- 
tion of  the  brain  and  the 
spinal  cord,  and,  with  few 
exceptions,  the  cerebro-spinal  nerves — namely,  those 
having  their  origin  in  the  brain  and  spinal  cord.  A 
medullated  fibre  is  composed  of  the  axis-cylinder,  the 
most  central  portion,  the  white  substance  of  Schwann, 
which  envelops  it,  and  the  primitive  sheath,  sometimes 
called  "  neurilemma,"  a  delicate  external  membrane  (Fig. 
45).  Of  all  these  .structures  the  axis-cylinder  is  the 
most  important ;  indeed,  it  is  an  essential,  as  without 
it  the  nerve  could  not  perform  its  functions.  The 
neurilemma  and  the  white  substance  are  not  always 
present  in  all  portions  of  a  medullated  nerve.  At  the. 
commencement  and  at  the  termination  they  arc  absent. 
The  size  of  the  medullated  fibres  is  very  variable.  In 
the  gray  sub.stance  of  the  spinal  cord  they  may  be  found, 


Fig.  45. — A,  three  medullated  nerve- 
fibres,  the  medullary  sheath  of  which 
is  stained  dark  with  osmic  acid  ;  N, 
nodes  of  Ranvier  ;  B,  two  non-med- 
ullated nerve-fibres,  with  nuclei  in  the 
primitive  sheath. 


220 


HUMAN  PHYSIOLOGY. 


having  a  diameter  of  2  m.mm.,  while  in  the  peripheral 
nerves  this  may  be  as  much  as   18  m.mm. 

(2)  Non-medidlated  fibres,  which  are  known  also  as 
"  gray  and  gelatinous  fibres  "  and  "  fibres  of  Remak," 
compose  the  olfactory  nerve  and  the  sympathetic  nerves, 
and  are  also  found  elsewhere.  As  their  name  implies, 
they  have  none  of  the  medullary  or  white  substance  of 
Schwann.  They  are  composed  of  fibrillae  within  a  sheath, 
the  former  being  the  axis-cylinder,  the  latter  the  neu- 
rilemma. Scattered  along  the  fibre  between  these  two 
structures  are  nuclei. 

Termination  of  Nerve-fibres. — Nerve-fibres  terminate 
in  various  ways.  In  voluntary  muscles  they  terminate 
in  end-plates,  fibres  from  which,  doubtless  representing 
the  axis-cylinders,  are  connected  with  the  contractile 
tissue  of  the  muscular  fibres.     In  involuntary  muscular 


Fig.  46. — Drawing  from  a  Section  of  Injected        Fig.   47. — End-bulb  from   Human 


Skin,  showing  three  papillje,  the  central  one 
containing  a  tactile  corpuscle  (ci),  connected 
with  a  meduUated  nerve,  and  that  at  each 
side  (c)  occupied  by  vessels  (Cadiat). 


Conjunctiva,  treated-with  osmic 
acid,  showing  cells  of  core  (Long- 
worth)  :  a,  nerve-fibre ;  b,  nucleus 
of  sheath;  c,  nerve-fibre  within 
core  ;  d,  cells  of  core. 


tissue   the   nerve-fibres   form   a  plexus   from  which  are 
given  off  smaller  fibres  that  are  ultimately  distributed  to 


NERVOUS  FUNCTIONS.  221 

the  nucleoli.  In  glands  the  nerve-fibres  end  in  secreting 
cells;  in  the  skin  some  terminate  in  the  hair-follicles  and 
others  in  the  epithelium.  Besides  these  nerve-fibres  there 
are  three  kinds  of  corpuscles  in  and  beneath  the  skin 
with  which  nerves  are  connected — namely  : 

( i)  TJic  corpuscles  of  Pacini,  which  are  constantly  found 
in  the  subcutaneous  tissue  of  the  palms  of  the  hands  and 
the  soles  of  the  feet,  and  are  sometimes  found  also  in 
other  situations,  such  as  the  dorsal  surface  of  the  hands 
and  feet,  and  the  nipples ; 

(2)  TJie  tactile  corpuscles  (Fig.  46),  which  are  present 
in  about  one  in  four  of  the  papillae  of  the  skin  of  the 
third  phalanx  of  the  index  finger,  are  found  also  in  other 
papillae,  but  not  in  such  great  proportion.  As  a  rule 
they  are  most  abundant  on  the  plantar  surface  of  the  feet; 

(3)  The  end-bulbs  (Fig.  47),  which  occur  in  the  con- 
junctiva, the  mouth,  the  tongue,  the  glans  penis,  and  the 
clitoris. 

Chemistry  of  Nervous  Matter. — The  chemical  com- 
position of  nervous  matter  is  by  no  means  thoroughly 
understood.  Among  its  constituents  are  cholesterin, 
lecithin,  cerebrin,  protagon,  and  neuro-keratin. 

Functions  of  Nerve-cells  and  Nerve-fibres. — The 
nerve-cells  receive  and  generate  impulses,  while  nerve- 
fibres  have  the  power  only  to  conduct  the  impulses. 

Classification  of  Nerve-centres. — A  collection  of 
nerve-cells,  whether  it  be  large  or  small,  is  a  nerve-centre 
or  ganglion.  In  such  a  centre  there  are,  besides  the  cells, 
blood-vessels,  nerve-fibres,  and  neuroglia,  but  the  cells 
are  the  characteristic  element  upon  which  the  function 
of  a  centre  depends.  These  centres  may  be  divided  into 
(i)  conscious;  (2)  reflex;  (3)  automatic;  (4)  relay;  and 
(5)  junction. 


222  HUMAN  PHYSIOLOGY. 

Conscious  nerve-centres  are  located  in  the  brain.  In 
them  the  sensation  of  pain  is  produced,  and  out  from 
them  go  the  impulses  which  result  in  voluntary  move- 
ments. 

Reflex  Nen>e-centres. — The  gray  matter  of  the  spinal 
cord  is  an  admirable  example  of  a  purely  reflex  centre. 
Impressions  reaching  it  by  the  sensory  roots  of  the 
spinal  nerves  excite  impulses  which  travel  out  along 
motor  nerves  to  muscles,  and  cause  them  to  contract. 
In  this  there  is  no  consciousness  ;  indeed,  in  an  animal 
that  is  decapitated  the  same  action  takes  place.  Reflex 
centres  are  found  also  in  the  brain. 

Automatic  nerve-cejitres  do  not  require  to  be  excited 
to  action  by  impulses  coming  to  them  through  afferent 
nerves,  as  is  the  case  with  the  reflex  centres,  but  they 
send  out  impulses  without  such  excitation.  The  cardio- 
inhibitory  centre  in  the  medulla  oblongata,  in  which  cen- 
tre originate  the  impulses  that  have  already  been  spoken 
of  as  being  sent  to  the  heart  through  the  pneumogastric, 
is  one  of  these. 

Relay  Nerve-centres. — When  a  feeble  impulse  reaches 
a  relay  centre,  that  centre  is  excited,  and  from  it  may  go 
out  very  powerful  impulses,  just  as  a  feeble  current  of 
electricity  may  bring  into  play  a  local  battery  which  will 
have  much  greater  power  than  the  current  which  brought 
it  into  action. 

Junction  nerve-centres  are  those  which  are  so  con- 
nected with  other  centres  that  an  impulse  exciting  one 
may  also  excite  the  other,  and  thus  impulses  may  be 
sent  to  several  regions  of  the  body. 

Classification  of  Nerve-fibres. — Nerve-fibres  con- 
duct impulses  from  within  outward  and  from  without 
inward.     Whether  it  is  the  function  of  a  given  nerve 


NERVOUS  FUNCTIONS.  223 

to  do  the  one  or  the  other  does  not  depend  upon 
anything  in  the  nerve  itself,  but  upon  its  relations; 
and  there  is  every  reason  to  believe  that  were  it  pos- 
sible to  separate  a  nerve  from  its  anatomical  connections 
and  attach  it  to  different  structures,  it  would  be  just  as 
capable  of  acting  in  its  new  relations  as  it  did  in  the 
old;  just  as  a  copper  wire  will  equally  well  carry  a 
current  of  electricity  to  ring  a  bell  or  to  supply  a  motor 
or  to  turn  a  hand  on  a  dial :  the  result  depends  not 
upon  the  wire,  but  upon  the  mechanism  with  which  it 
is  in  connection. 

Studying  nerves,  then,  as  they  are  actually  found  in 
the  body,  it  will  be  found  that  there  are  some  which 
carry  impulses  outward  from  nerve-centres;  these  are 
efferent  nerves.  Inasmuch  as  the  impulse  is  going  away 
from  the  centre,  they  are  also  called  "  centrifugal 
nerves ;"  those  which  carry  impulses  from  the  periphery 
to  the  centres  are  called  "  afferent "  or  "  centripetal 
nerves ;"  while  a  third  class  comprise  those  which 
connect  nerve-centres  with  one  another,  and  are  called 
"  intercentral  nerves." 

Bflterent  nerves  were  formerly  spoken  of  as  motor 
nerves,  and  indeed  even  now  some  writers  use  the  terms 
efferent  and  motor  as  synonyms.  All  motor  nerves  are 
efferent,  for  they  carry  impulses  outward,  but  all  efferent 
nerves  are  not  motor  nerves.  A  nerve  which  carries  an 
impulse  to  a  muscle,  and  thus  brings  about  motion,  is 
properly  called  a  "  motor  nerve ;"  but  one  that  conducts 
an  impulse  to  a  gland,  the  result  of  which  is  the  activity 
of  its  cells  and  the  production  of  a  secretion,  is  improp- 
erly named  a  motor  nerve,  although  it  is  unquestionably 
an  efferent  nerve.  Secretory  is  a  much  more  expressive 
name.     Efferent  nerves  maybe  divided  as  follows:  (i) 


224  HUMAN  PHYSIOLOGY. 

motor;  (2)  vaso-motor;  (3)  secretory ;  (4)  trophic ;  and 
(5)  inhibitory. 

Motor  nerves  terminate  in  muscles,  and  convey  to  them 
impulses  which  cause  and  regulate  their  contraction. 

Vaso-motor  nerves,  although  distributed  to  the  muscu- 
lar tissue  of  blood-vessels,  and  thus  act  as  motor  nerves, 
regulate  the  amount  of  blood  supplied  to  a  part,  and 
it  seems  wise  to  separate  them  from  the  purely  motor 
nerves  and  put  them  in  a  class  by  themselves. 

Secretory  Nerves. — The  impulses  which  these  nerves 
carry  to  glands  bring  about  their  secretion.  The  chorda 
tympani  is  a  striking  example. 

Trophic  nerves  are  supposed  by  some  to  govern  the 
nutrition  of  the  structures  to  which  they  are  distributed 
entirely  independently  of  the  regulation  of  the  blood- 
supply.  It  is  still  a  mooted  question  whether  such 
nerves  exist.  The  subject  will  be  again  discussed  in 
the  consideration  of  the  functions  of  the  fifth  pair  of 
cranial  nerves. 

Efferent  inhibitory  nerves  carry  outward  impulses  which 
restrain  or  inhibit  the  action  of  the  organs  to  which  they 
are  distributed.  The  pneumogastric,  so  far  as  the  heart 
is  concerned,  is  such  a  nerve.  Without  its  restraining 
influence  the  heart  would  beat  much  faster. 

Afferent  nerves  in  some  physiological  works  are 
called  "  sensory  nerves,"  but  there  is  the  same  impro- 
priety in  using  these  terms  synonymously  as  in  the  case 
of  efferent  and  motor  nerves.  All  sensory  nerves  are 
afferent,  but  all  afferent  nerves  are  not  sensory.  Affer- 
ent nerves  may  be  divided  as  follows,  although  the  dis- 
tinction is  by  no  means  so  well  marked  as  in  the  efferent 
nerves:  (i)  sensory;  (2)  nerves  of  special  sense;  (3) 
thermic  nerves  ;  (4)  excito-reflex  ;  and  (5)  inhibitory. 


NERVOUS  FUNCTIONS.  225 

(i)  Sensory  Ncn<cs. — When  these  nerves  are  stimu- 
lated an  impulse  is  carried  to  the  brain,  which  there 
gives  rise  to  a  conscious  sensation  that  may  amount  to 
pain. 

(2)  Nerves  of  Special  Sense. — The  impulses  carried 
by  these  nerves  do  not  give  rise  to  pain,  but  with  each 
nerve  is  connected  a  special  sensation  :  with  the  olfactory, 
the  sense  of  smell ;  with  the  optic,  the  sense  of  light ;  and 
with  the  auditory,  the  sense  of  hearing. 

(3)  Thermic  Nerves. — It  is  believed  by  some  writers 
that  these  are  special  nerves  which  convey  the  sense  of 
temperature  only,  but  this  is  still  an  unsettled  question. 

(4)  Excito-reflex  Ncwes. — In  these  nerves  there  is  an 
impulse  carried  to  a  nerve-centre  without  producing  a 
conscious  sensation  :  this  centre  is  excited,  and  from  it 
or  from  another  centre  with  which  it  is  in  communica- 
tion there  goes  out  an  impulse  that,  if  it  be  a  gland  to 
which  it  is  distributed,  produces  secretion.  Such  a  nerve 
would  be  an  excito-secretory  nerve ;  or  if  it  be  distrib- 
uted to  a  muscle  it  produces  motion,  and  would  in  that 
case  be  considered  an  excito-motor  nerVe. 

(5)  Afferent  Inhibitory  Nerves. — The  afferent  inhibitory 
nerves  are  also  called  "  centro-inhibitory  "  to  distinguish 
them  from  the  efferent  inhibitory  nerves.  The  centro-in- 
hibitory nerves  carry  impulses  to  nerve-centres,  which  are 
so  affected  as  to  prevent  them  from  sending  out  impulses. 
A  familiar  instance  is  that  of  pinching  the  lip  to  prevent 
sneezing.  It  is,  however,  doubtful  whether  there  exists 
a  separate  class  of  nerves  performing  this  function,  rather 
than  ordinary  sensory  fibres  which  act  in  this  peculiar 
manner  for  the  moment. 

Intercentral  Nerves. — The  nerve-centres  are  intimately 
connected  with  one  another  by  nerves  which  are  neither 

16 


226  HUMAN  PHYSIOLOGY. 

afferent  nor  efferent,  and  which  are  called  "  intercentral 
fibres."  As  has  already  been  said,  even  the  simplest 
movements  of  the  body  bring  into  action  several,  and 
sometimes  many,  muscles;  of  course  this  action  is 
more  obvious  in  complex  movements.  To  accomplish 
this  various  nerve-centres  must  be  at  work,  and  that 
they  may  act  harmoniously  and  produce  co-ordinated 
movements  they  are  required  to  be  in  intimate  relation- 
ship. Study  for  a  moment  the  intricate  mechanism 
brought  into  play  in  the  ordinary  act  of  picking  up  a 
pin  from  the  floor,  and  it  will  be  readily  understood  how 
essential  it  is  that  the  nerve-centres  responsible  for  these 
movements  should  act  in  the  most  perfect  harmony,  send- 
ing to  each  muscle  just  the  right  amount  of  nerve-force 
and  at  exactly  the  right  moment ;  otherwise  the  act  could 
not  be  accomplished  in  the  perfect  manner  that  it  is. 

Nerve-stimuli. — Nerve-fibres  have  no  power  of  receiv- 
ing or  generating  impulses  :  they  are  simply  conductors. 
It  is  extremely  difficult  to  define  a  nerve-impulse.  If 
certain  nerves  are  acted  on  in  the  proper  manner  at  their 
peripheral  extremities,  there  is  produced  in  the  nerve  a 
certain  change  which  manifests  itself  at  the  distal  ex- 
tremities :  the  something  which  acts  upon  these  nerves 
is  called  a  "  stimulus,"  and  that  which  travels  along  the 
nerve  is  called  a  "  nervous  impulse."  It  has  been  as- 
sumed that  this  is  a  molecular  change  in  the  axis-cylin- 
der. Stimuli  may  excite  nerve-centres  from  which  im- 
pulses travel  outward  along  efferent  nerves,  or  they  may 
excite  the  end-organs  of  nerves,  and  the  impulses  they 
generate  may  travel  inward  along  afferent  fibres  to  the 
centres.  Besides,  a  nerve  may  be  stimulated  at  any 
point  between  its  ends.  A  current  of  electricity  applied 
to  a  motor  nerve  at  any  such  point  will  cause  contrac- 


NERVOUS  FUNCTIONS.  22/ 

tion  of  the  muscles  to  which  it  is  distributed,  as  if  the 
stimulus  had  been  applied  to  its  origin.  In  the  same 
way,  if  a  sensitive  nerve  were  to  be  stimulated,  the  sen- 
sation would  be  felt  as  if  the  stimulus  had  been  applied 
to  its  end.  Thus,  if  the  ends  of  the  nerves  in  a  stump 
resulting  from  an  amputation  of  the  arm,  for  instance,  be 
pressed  upon  by  the  scar-tissue  which  forms,  it  will  seem 
to  the  individual  affected  that  the  pain  is  in  the  fingers, 
the  sensation  being  referred  to  the  parts  in  which  the 
nerves  originally  terminated. 

Classification  of  Nerve-stimuli. — Nerve-stimuli  are 
general  and  special.  The  former  excite  all  nerves,  while 
the  latter  excite  only  special  nerves. 

General  nervc-stbmdi  are  electrical,  chemical,  mechan- 
ical, and  thermal.  A  current  of  electricity  in  the  form 
of  a  shock  will  stimulate  a  nerve;  a  blow  will  do  the 
same;  so  also  will  some  chemical  substances.  Heat  or 
cold  suddenly  applied  will  produce  a  similar  effect. 

Special  Nerve-stimuli. — Light  affects  only  the  optic 
nerve,  and  sound  only  the  auditory  nerve ;  hence  light 
and  sound  are  special  nerve-stimuli.  Other  special 
stimuli  excite  the  nerves  of  smell  and  taste. 

The  rate  at  zvhich  impulses  travel  along  the  human 
motor  nerves  is  about  33  metres  per  second. 

2.  General  Arrangement  of  the   Nervous   System. 

The  nervous  system  is  divided  into  two  subdivisions  : 
(i)  the  cerebro-spinal  system,  and  (2)  the  sympathetic 
system. 

The  cerebro-spinal  system  includes  the  brain  and 
spinal  cord,  which  together  form  the  cerebro-spinal  axis, 
and  the  nerves  which  come  from  them — namely,  the 
cranial  and  spinal  nerves. 


228  HUMAN  PHYSIOLOGY. 

Spinal  Cord. — The  spinal  cord  is  situated  in  the  ver- 
tebral canal,  and  is  covered  by  three  membranes — the 
dura  mater,  arachnoid,  and  pia  mater.  It  is  about  0.43 
metres  in  length,  and,  in  general,  is  of  a  cylindrical 
shape  ;  it  weighs  42.5   grammes. 

Enlargemejits  of  the  Spinal  Cord. — Two  enlargements 
along  the  course  of  the  spinal  cord  are  noteworthy. 
The  cervical  enlargement  extends  from  the  third  cer- 
vical to  the  first  or  the  second  dorsal  vertebra,  and  the 
lumbar  enlargement  is  at  the  eleventh  and  twelfth  dor- 
sal vertebrae.  From  the  cervical  enlargement  go  off  the 
nerves  which  supply  the  upper,  and  from  the  lumbar 
those  which  supply  the  lower,  extremities. 

Fissures. — On  the  anterior  surface  of  the  spinal  cord  is 
a  groove,  the  anterior  median  fissure,  which  extends  to 
the  anterior  white  commissure.  On  the  posterior  surface 
is  also  a  fissure,  the  posterior  median  fissure,  which  is 
not  so  wide  as  the  anterior,  but  is  deeper,  extending  to 
the  posterior  gray  commissure.  It  will  thus  be  seen 
that  the  anterior  and  posterior  fissures  nearly  divide  the 
cord  into  two  symmetrical  halves,  which  are  connected 
by  the  commissure. 

At  a  little  distance  from  the  anterior  median  fissure  on 
each  side  is  the  antero-lateral  fissure.  Strictly  speaking, 
this  is  not  a  fissure,  being  rather  a  line  of  small  openings 
at  which  emerge  the  anterior  roots  of  the  spinal  nerves. 
Between  the  antero-lateral  fissure  and  the  anterior  me- 
dian fissure  the  white  matter  of  the  cord  is  called  the 
"  anterior  column."  In  front  of  the  posterior  median 
fissure  and  on  either  side  is  the  postero-lateral  fissure. 
Here  emerge  the  posterior  roots  of  the  nerves.  The 
white  matter  between  the  origins  of  the  two  sets  of  roots 
is  called  the  "  lateral  column."     The  anterior  and  lateral 


NERVOUS  FUNCTIONS. 


229 


columns  are  together  sometimes  denominated  "  antero- 
lateral."    Between  the  postero-lateral  and  posterior  me- 


FiG.  48. — Different  Views  of  a  Portion  of 
the  Spinal  Cord  from  the  cervical  region, 
with  the  roots  of  the  nerves.  Tn  A 
the  anterior  surface  of  the  specimen  is 
shown,  the  anterior  nerve-root  of  its 
right  side  being  divided  ;  in  .S  a  view  of 
the  right  side  is  given  ;  in  C  the  upper 
surface  is  shown ;  in  D  the  nerve-roots 
and  ganglion  are  shown  from  below : 
I,  the  anterior  median  fissure;  2,  poste- 
rior median  fissure  ;  3,  anterior  lateral  de- 
pression, over  which  the  anterior  nerve- 
roots  are  seen  to  spread ;  4,  posterior 
lateral  groove,  into  which  the  posterior 
roots  are  seen  to  sink;  5,  anterior  roots 
passing  the  ganglion  :  5',  in  A,  the  ante- 
rior root  divided ;  6,  the  posterior  roots, 
the  fibres  of  which  pass  into  the  ganglion, 
6;  7,  the  united  or  compoimd  nerve; 
7',  the  posterior  primary  branch,  seen 
in  A  and  D  to  be  derived  in  part  from  the 
anterior  and  in  part  from  the  posterior 
root  (Allen  Thomson). 


Fig.  49. — Transverse  Section  of  Half 
the  Spinal  Cord,  in  the  lumbar  en- 
largement (semi-diagrammatic) :  i,  an- 
terior median  fissure ;  2,  posterior 
median  fissure  ;  3,  central  canal  lined 
with  epithelium  ;  4,  posterior  com- 
missure;  5,  anterior  commissure; 
6,  posterior  column ;  7,  lateral  col- 
umn :  8,  anterior  column  (the  white 
substance  is  traversed  by  radiating 
trabeculse  of  pia  mater) ;  9,  fasciculus 
of  posterior  nerve-root,  entering  in 
one  bundle  ;  10,  fasciculi  of  anterior 
roots,  entering  in  four  spreading  bun- 
dles of  fibres  :  /',  in  the  cervix  cornu, 
decussating  fibres  from  the  nerve-roots 
and  posterior  commissure  ;  c,  poste- 
rior vesicular  columns.  About  half- 
way between  the  central  canal  and  7 
are  seen  the  group  of  nerve-cells  form- 
ing the  tractus  intermedio-lateralis  ; 
e,e,  fibres  of  anterior  roots  ;  c',  fibres 
of  anterior  roots  which  decussate  in 
anterior  commissure  (Allen  Thom- 
son). 


dian  fissure  is  the  posterior  column.     A  subdivision  of 
this  column  is  indicated  by  a  slight  groove,  giving  rise 


230  HUMAN  PHYSIOLOGY. 

to  the  designation  of  that  portion  between  this  groove 
and  the  fissure  as  the  posterior  median  column. 

Section  of  the  Spinal  Cord. — A  cross-section  of  the 
spinal  cord  shows  a  central  gray  substance  and  an  ex- 
ternal white  substance.  The  gray  matter  presents  the 
appearance  of  two  crescents,  with  the  concavities  out- 
ward, joined  together  by  a  band  of  gray  matter,  the 
gray  commissure.  The  points  of  the  crescents  are  the 
horns  or  cornua,  two  anterior  and  two  posterior.  The 
posterior  cornua  come  nearly  to  the  surface  of  the  cord 
at  the  postero-lateral  fissure,  while  between  the  surface 
and  the  extremities  of  the  anterior  cornua  there  is  con- 
siderable white  matter.  The  arrangement  of  the  white 
matter  into  columns  is  readily  discerned  in  this  section. 
In  the  gray  commissure  is  a  small  canal — the  central 
canal — which  is  only  of  interest  in  connection  with  the 
development  of  the  cord.  That  portion  of  the  commis- 
sure in  front  of  the  canal  is  the  anterior  gray,  and  that 
behind  the  posterior  gray,  commissure.  Sections  of  the 
cord  at  different  levels  show  that  the  white  substance  is 
most  abundant  in  the  upper  part,  and  gradually  becomes 
less  abundant  as  the  examination  is  made  down  the 
cord.  The  cervical  and  lumbar  enlargements  are  due 
to  the  increased  amount  of  gray  matter  at  these  points. 

Minute  Structure  of  the  Cord. — Neuroglia  supports 
both  the  white  and  gray  matter  of  the  spinal  cord. 
The  white  matter  is  composed  of  medullated  nerve- 
fibres,  together  with  blood-vessels,  running  longitudi- 
nally, except  that  in  the  white  commissure  they  run 
transversely,  and  when  traced  are  seen  to  pass  from  the 
anterior  horn  of  one  side  to  the  anterior  column  of  the 
other  side,  the  fibres  from  each  side  crossing  those  from 
the  other,  forming  a  decussation.     By  this  means  each 


NERVOUS   FUNCTIONS. 


231 


anterior  column  is  connected  with  the  gray  matter  of 
the  opposite  side.  There  are  also  fibres  passing  in  a 
more  or  less  transverse  direction  from  the  gray  matter 
to  the  roots  of  the  nerves,  and  from  the  gray  matter  to 
the  columns,  into  which  they  enter  and  probably  become 
longitudinal. 

Tracts  in  the  Cord. — The  columns  of  the  spinal  cord 
have  been  shown  to  be  made  up  of  separate  collections 
of  fibres  called  "  tracts,"  and 
there   is   every   reason   to  be- 
lieve that  each  of  these  tracts     , ,  ^ 
has  its  own  peculiar  function,    /a.^ 
These  tracts  are  as  follows  :         V^^a^^-' 

I.    The     direct     pyramidal 
tract,  or  fasciculus  of  Turck,  p.root     p.m.c. 

is  the  anterior  portion  of  the   Fig.  50.— Diagram  of  the  Spinai  Cord, 

,  '  ^   , ,  at  the  lower  cervical  region,  to  show 

anterior  column,  next  the  an-      ^^^  ^^^^^  ^^  Abres:  d.p.t.,  direct 

pyramidal  tract ;  D.  C.  T.,  direct 
cerebellar  tract;  P.M.  C,  posterior 
median  column;  A.  G.F.,  anterior 
ground  fibres;  A.C.,  anterior  com- 
missure; P.C.,  posterior  commis- 
sure; A.L.A.  T.,  antero-Iateral  as- 
cending tract;  Ant.  C,  anterior  cor- 
nu  ;  P.  Cor.,  posterior  cornu  ;  C.C. 
P.,  intermediate  gray  substance; 
L.  L.  L.,  lateral  limiting  layer  (af- 
ter Gowers). 


terior  median  fissure,  and  is 
continuous  with  the  fibres  of 
the  pyramid  of  the  medulla 
oblongata  on  the  same  side. 
This  tract  gradually  becomes 
smaller  and  disappears  in  the 
middle  of  the  dorsal  region 
of  the  cord. 

2.  The  fundamental  fasciculus  is  the  remaining  portion 
of  the  anterior  column; 

3.  The  anterior  radicular  zone  ; 

4.  The  mixed  lateral  column  ; 

5.  The  crossed  pyramidal  fasciculus; 

6.  The  cerebellar  Cf)lumn.  The  last  four  tracts  compose 
the  lateral  column.  The  fibres  of  the  cros.sed  pyramidal 
fasciculus,  as  the  name  implies,  are  continuous  with  the 


232  HUMAN  PHYSIOLOGY. 

decussating  fibres  of  the  pyramid  of  the  medulla,  while 
those  of  the  cerebellar  column  connect  with  the  cere- 
bellum. 

7.  The  column  of  Goll,  which  is  a  part  of  the  poste- 
rior column,  is  situated  next  to  the  posterior  median  fis- 
sure. Outside  of  this,  and  making  up  the  rest  of  the 
posterior  column,  is 

8.  The  column  of  Burdach,  or  cuneate  fasciculus. 
Columns  7  and  8  can  both  be  traced  into  the  medulla. 

The  gray  mailer  of  the  spinal  cord  is  composed  of 
nerve-cells,  nerve-fibres,  neuroglia,  and  blood-vessels. 
The  large  nerve-cells  are  multipolar,  some  having  as 
many  as  eight  processes,  and  they  are  aggregated  to 
form  groups.  One  of  these  groups,  situated  in  the 
anterior  horn,  is  the  vesicular  column  of  the  anterior 
cornu.  It  is  in  reality  two  groups — one  in  the  middle 
near  the  anterior  column,  and  the  other  laterally  situated 
near  the  lateral  column.  Another,  Clarke's  posterior 
vesicular  column,  is  situated  at  the  base  of  the  posterior 
column  toward  the  inner  side.  A  third  collection  of 
cells  is  the  intermedio-lateral  tract  at  the  external  part 
of  the  gray  matter,  where  the  anterior  and  posterior 
cornua  join.  The  small  nerve-cells  are  found  through- 
out the  gray  matter,  and  not  in  groups  as  are  the  larger 
cells. 

The  nerve-fibres  of  the  gray  matter  are,  as  a  rule, 
smaller  than  those  in  the  columns.  In  the  posterior 
cornua  they  form  Gerlach's  nerve-network,  very  small 
fibres  together  with  larger  ones.  The  fibres  of  this  net- 
work can  be  traced  to  the  fibres  of  the  posterior  nerve- 
roots,  and  also  to  the  processes  of  nerve-cells  occupying 
an  intermediate  position.  In  the  anterior  cornua  some 
of  the  processes  of  the  nerve-cells  communicate  directly 


NERVOUS  FUNCTIONS.  233 

with  the  fibres  of  the  anterior  nerve-roots,  and  others 
with  the  nerve-network  of  Gerlach.  The  neurogha  at 
the  tip  of  the  posterior  cornu  is,  from  its  gelatinous 
character,  called  "substantia  gelatinosa." 

Spinal  Nerves. — From  the  spinal  cord  pass  off  thirty- 
one  pairs  of  spinal  nerves,  which  are  distributed  to  the 
neck,  the  trunk,  and  the  extremities.  Each  nerve  is 
made  up  of  an  anterior  (small)  and  a  posterior  (large) 
nerve-root.  The  latter  is  characterized  anatomically  by 
having  upon  it  a  ganglion.  Beyond  the  ganglion  the 
roots  unite,  forming  a  mixed  nerve. 

Functions  of  Spinal  Nerves. — Stimulation  of  an  ante- 
rior root  causes  contraction  in  the  muscle  to  which  it  is 
di.stributed,  while  its  division  is  followed  by  a  loss  of 
motion  in  the  same  muscle.  In  neither  instance  is  sen- 
sation affected.  If  after  the  division  the  distal  portion 
of  the  nerve  be  stimulated,  muscular  contraction  will 
follow,  while  stimulation  of  the  proximal  end,  that  which 
is  in  connection  with  the  cord,  will  produce  no  effect. 
The  anterior  roots  are  therefore  efferent  and  motor,  and 
are  distributed  to  muscles. 

Stimulation  of  a  posterior  root  causes  a  sensation  of 
pain  in  the  part  to  which  the  nerve  is  distributed.  Division 
of  the  root  causes  a  loss  of  sensation  in  that  part.  If  after 
division  the  distal  portion  of  the  nerve  be  stimulated,  no 
effect  is  produced,  while  stimulation  of  the  proximal  por- 
tion produces  sensation.  The  posterior  roots  are  there- 
fore afferent  and  sensory,  and  are  distributed  to  the  skin. 
The  two  roots  uniting  form  a  mixed  nerve ;  that  is,  one 
in  which  there  are  both  motor  and  sensory  fibres. 

Recurrent  Sejisibility . — When  the  distal  end  of  a  di- 
vided anterior  root  is  stimulated,  besides  the  muscular 
contraction  which  follows  there  is  also  some  pain  pro- 


234  HUMAN  PHYSIOL  OGY. 

duced.  If  the  trunk  of  the  nerve  beyond  the  ganglion 
be  divided,  and  then  the  anterior  root  be  stimulated,  no 
muscular  contraction  results,  but  the  pain  is  felt  as 
before.  If,  however,  the  posterior  root  be  divided,  no 
sensation  is  produced.  The  sensation  experienced  when 
the  anterior  root  is  stimulated  is  accounted  for  by  the 
presence  in  this  root  of  some  sensory  fibres  which  pass 
up  into  it  for  a  short  distance  and  form  a  loop,  returning 
to  the  junction  of  the  two  roots,  and  then  pursuing  their 
course  in  the  posterior  root.  These  are  called  "  recurrent 
sensory  fibres."  The  impulse  passes  down  these  fibres  to 
the  point  of  junction  of  the  two  roots,  and  then  along 
the  posterior  root  to  the  nerve-centre. 

Functiofi  of  the  Spinal  Ganglia. — As  has  already  been 
stated,  upon  each  posterior  root  of  a  spinal  nerve  is  a 
ganglion.  When  examined  under  the  microscope  the 
root-fibres  spread  out,  passing  between  groups  of  large 
cells  having  prominent  nuclei  and  a  diameter  of  about 
lOO  m.mm.  With  one  of  these  ganglion-cells  a  root-fibre 
is  in  communication,  and  the  function  of  these  cells  is 
doubtless  to  regulate  the  nutrition  of  the  fibres  con- 
nected with  them.  They  are  true  trophic  centres,  if  any 
such  are  to  be  found  in  the  body,  a  matter  still  in  dis- 
pute. 

Connection  of  the  Nerve-roots  with  the  Cord:  Anterior 
or  Motor  Roots. — The  fibres  of  the  anterior  root  may  be 
traced  through  the  fibres  of  the  antero-lateral  column 
into  the  anterior  cornu,  where  they  separate,  (i)  Some 
pass  through  the  anterior  commissure  to  the  opposite 
side,  where  they  terminate  in  the  axis-cylinder  processes 
of  the  large  multipolar  cells  of  the  anterior  cornua;  (2) 
others  end  in  the  middle  group  of  cells  in  the  anterior 
column  of  the  same  side ;  (3)  others  are  traced  to  the 


NERVOUS  FUNCTIONS.  235 

axis-cylinder  processes  of  the  cells  of  the  lateral  group 
of  the  vesicular  column  of  the  anterior  cornu  ;  (4)  others 
pass  through  the  gray  matter,  and  emerge  from  it  to 
enter  the  lateral  column,  where  they  become  longitudi- 
nal fibres;  (5)  others  pass  backward  to  become  con- 
nected with  the  axis-cylinders  of  the  cells  of  Clarke's 
column  at  the  base  of  the  posterior  cornu. 

Posterior  or  Sensory  Root. — These  fibres  enter  the  pos- 
terior cornua:  (i)  Some  become  vertical,  while  (2)  others 
cross  over  to  the  other  side  through  the  posterior  com- 
missure, and  (3)  others  pass  into  the  anterior  cornu  of 
the  same  side. 

Fu)ictio)is  of  the  Spinal  Cord  as  a  Conductor  of  Im- 
pulses.— The  spinal  cord  is  the  principal  channel  through 
which  all  impulses  from  the  trunk  and  the  extremities 
pass  to  the  brain,  and  all  impulses  to  the  trunk  and 
extremities  pass  from  the  brain.  If  through  disease  or 
injury  the  cord  be  disorganized  at  any  point,  all  power 
to  produce  voluntary  motion  in  the  parts  below  the  in- 
jury is  lost,  and  conscious  sensation  in  these  parts  is 
from  that  moment  abolished.  The  cord  therefore  acts 
as  a  conductor  of  impulses,  both  motor  and  sensory, 
between  the  brain  and  the  trunk  and  the  extremities. 
From  the  description  already  given  of  the  course  the 
motor  and  sensory  fibres  take  in  the  cord,  it  would  nat- 
urally be  inferred  that  the  different  kinds  of  impulse 
which  they  carry  follow  different  paths  in  the  cord. 

Methods  of  Examination. — The  identity  in  the  struc- 
ture of  nerves,  whether  motor  or  sensory,  and  the  vast 
number  of  nerves  in  the  cord,  make  it  impossible  to 
trace  with  the  ey*,  even  aided  by  the  microscope  and 
the  most  careful  dissection,  the  course  of  nerve-fibres  for 
any  distance.     Several  methods  have  been  developed  by 


236  HUMAN  PHYSIOLOGY. 

patient  investigators  which  have  done  much  toward  solv- 
ing this  most  difficult  problem  of  the  position  which  the 
different  fibres  occupy.  The  most  important  is  the  de- 
generative method. 

Des^enerative  Method. — When  a  nerve  is  divided  the 
first  result  is  a  loss  of  its  function.  Afterward  the  nerve 
undergoes  degeneration,  which  results  in  changes  in  its 
structure  that  can  readily  be  seen.  Thus  the  course  of 
a  nerve  or  a  collection  of  nerves  may  be  traced  through- 
out its  entire  extent.  These  changes  are  believed  to  be 
due  to  the  severance  of  the  nerve  from  its  trophic  centre. 
If  an  anterior  root  of  a  spinal  nerve  be  divided,  the  dis- 
tal end,  being  separated  from  the  gray  matter  of  the 
cord  which  is  its  centre  of  nutrition,  undergoes  degen- 
eration, while  the  end  which  remains  connected  with  the 
cord  retains  its  integrity.  If  a  posterior  root  be  divided 
between  the  cord  and  the  ganglion,  the  degeneration 
takes  place  between  the  cord  and  the  ganglion,  while  if 
divided  below  the  ganglion,  the  degeneration  takes  place 
in  that  portion  separated  from  the  ganglion,  showing 
that  the  ganglion  is  the  nutritive  centre  for  the  posterior 
root. 

This  same  method  is  used  to  study  the  course  of  the 
fibres  of  the  cord,  and  as  a  result  it  has  been  found  that 
they  degenerate  in  the  direction  in  which  the  impulses 
travel — namely,  that  if  those  fibres  which  carry  impulses 
downward  be  divided,  the  degeneration  takes  place  in 
the  same  direction,  while  the  reverse  is  true  for  those 
which  carry  impulses  upward. 

Condticting-paths  in  the  Cord. — The  paths  by  which 
voluntary  motor  impulses  traverse  tha  cord  are  fairly  well 
ascertained.  These  impulses  originate  in  the  brain  and 
pass  through  the  pyramids  in  the  medulla,  crossing  princi- 


NERVOUS  FUNCTIONS.  237 

pally  at  the  decussation  of  the  pyramids,  and  to  a  less 
degree  in  the  upper  part  of  the  cord,  to  the  opposite 
side,  whence  they  follow  the  course  of  the  pyramidal 
tracts,  direct  and  crossed,  terminating  in  the  cells  of  the 
anterior  cornua,  from  which  the  anterior  roots  arise  to 
be  distributed  to  the  muscles. 

The  course  pursued  by  the  sensory  impulses  is  not  so 
well  understood  ;  indeed,  opinions  differ  very  materially. 
It  was  formerly  held  by  many  of  the  best  investigators 
that  the  sensory  impulses  crossed  in  the  cord,  but  at  the 
present  time  the  evidence  is  accumulating  that,  as  with 
motor  impulses,  so  sensory  impulses  cross  mainly  in  the 
medulla  and  to  a  less  degree  in  the  cord.  That  both 
motor  and  sensory  impulses  do  cross  is  shown  by  the 
fact  that  whenever  there  is  a  lesion  of  the  brain  resulting 
in  paralysis  either  of  motion  or  of  sensation,  the  paral- 
ysis is  on  the  side  of  the  body  opposite  to  that  of  the 
lesion. 

In  reference  to  the  routes  taken  by  the  various  sen- 
sory impulses,  as  those  of  pain,  temperature,  touch,  etc., 
the  evidence  is  so  conflicting  that  it  would  be  confusing 
to  give  it.  Besides  the  function  which  the  cord  performs 
as  a  conductor  of  motor  and  sensory  impulses  by  virtue 
of  its  nerve-fibres,  it  also  acts  as  a  nerve-centre  in  which, 
by  virtue  of  its  nerve-cells,  afferent  impulses  are  received 
and  motor  impulses  are  generated. 

The  Spinal  Cord  as  a  Nerve-centre. — Voluntary  motion 
in  the  extremities,  which  motion  originates  in  the  brain, 
is  abolished  when  the  cord  is  divided  and  its  anatomical 
connection  with  the  brain  cut  off,  but  there  still  remains 
the  power  of  exciting  muscular  contractions  in  these 
muscles,  due  to  the  cells  of  the  cord  itself 

Reflex  Action. — If  a  frog  be  decapitated,   it  has  no 


238  HUMAN  PHYSIOLOGY. 

longer  the  power  of  producing  voluntary  movements, 
but  if  the  skin  of  a  foot  be  irritated  by  pinching,  the 
foot  is  pulled  away  from  the  source  of  irritation.  A 
slight  pinch  will  cause  only  the  one  foot  to  be  with- 
drawn, but  if  it  be  stronger  the  other  foot  may  also  be 
withdrawn.  This  is  an  instance  of  reflex  action.  Such 
movements  are  not  spontaneous,  but  they  require  the 
application  of  a  stimulus  for  their  production.  The  irri- 
tation does  not  act  upon  the  muscles  directly,  but  through 
the  medium  of  nerves,  an  afferent  nerve  carrying  the 
sensory  impulse  inward  to  the  cord,  and  an  efferent  nerve 
conducting  a  motor  impulse  outward  to  the  muscles. 
If  either  of  these  nerves  be  divided,  the  action  does  not 
take  place,  nor  does  it  if  the  gray  matter  be  broken  up. 
For  the  performance  of  a  reflex  act,  therefore,  three 
things  are  necessary — an  afferent  nerve,  a  nerve-centre, 
and  an  efferent  nerve,  all  in  a  physiological  condition. 

In  the  human  subject,  when  the  cord  is  injured  or 
diseased  at  any  point,  so  as  to  cut  off  communication 
between  the  brain  and  extremities,  but  is  still  intact 
below  this  point,  tickling  of  the  soles  of  the  feet  will 
be  followed  by  their  withdrawal,  although  the  individual 
will  be  entirely  unconscious  of  any  sensation.  This  is 
also  an  instance  of  reflex  action.  As  in  the  frog,  so  in 
man,  the  three  structures  mentioned  must  exist  in  a 
state  of  integrity  for  the  performance  of  this  act. 

It  is  not  essential  that  the  cord  be  diseased  in  order  to 
have  it  manifest  reflex  action.  Thus  if  the  hand  come 
in  contact  with  a  flame,  it  is  immediately  withdrawn. 
This  is  not  a  voluntary  act,  for  the  act  of  withdrawal 
takes  place  before  the  sensation  of  pain  is  felt  in  the 
brain.  It  is  a  purely  reflex  act,  in  which  the  gray  matter 
of  the  cord,  after  being  stimulated  by  an  impulse  carried 


NERVOUS  FUNCTIONS.  239 

to  it  by  an  afferent  nerve,  generates  an  impulse  which  is 
conveyed  by  an  efferent  nerve  to  the  muscles  concerned 
in  withdrawing  the  arm.  If  the  attention  were  fixed 
upon  the  subject  at  the  time  the  burn  was  received,  it 
might  be  possible  to  prevent  the  withdrawal.  This 
would  be  an  instance  of  inhibition  of  reflex  action. 
During  sleep  there  take  place  many  reflex  acts  which 
do  not  occur  in  a  waking  condition.  Thus  tickling  the 
feet  during  sleep  may  result  in  their  withdrawal ;  when 
the  tickling  is  practised  during  wakefulness  the  reflex 
act  can,  by  the  influence  of  the  will,  be  inhibited. 

This  power  of  the  spinal  cord  to  respond  to  afferent 
impulses  independently  of  the  will  is  of  great  advantage 
in  preserving  the  body  from  injury.  The  closing  of  the 
eye  when  moving  objects  are  liable  to  injure  it,  the  at- 
tempt to  retain  one's  equilibrium  after  slipping  on  the 
sidewalk,  the  raising  of  the  arms  in  front  of  the  face  to 
ward  off  an  unexpected  blow,  are  all  instances  of  this 
action. 

Walking,  playing  on  musical  instruments,  and  sim- 
ilar acts  are  all  performed  under  the  influence  of  the 
gray  matter  of  the  cord.  To  start  them  requires  the 
action  of  the  brain,  but  when  once  they  are  begun  their 
continuance  is  accomplished  by  the  cord,  and  the  brain 
can  be  busy  about  other  things  without  interfering  in 
the  slightest  degree  with  the  perfection  of  their  perform- 
ance. Indeed,  any  attempt  to  control  them  is  more  apt 
to  hinder  than  to  help  them.  Thus  in  coming  rapidly 
down  a  flight  of  steps,  if  the  spinal  cord  be  permitted  to 
take  entire  charge  of  the  act  the  descent  will  be  made 
with  ease  and  safety,  but  if  each  step  be  made  as  the 
result  of  volition,  the  chances  of  stumbling  or  of  tripping 
are  very  much  increased. 


240  HUMAN  PHYSIOLOGY. 

The  reflex  action  of  the  cord  may  be  diminished  by 
shock  to  the  nervous  system  ;  thus  in  the  frog  imme- 
diately after  decapitation  the  reflex  power  cannot  be  ex- 
cited, but  after  a  short  time  it  manifests  itself  under  the 
influence  of  a  stimulus.  A  similar  diminution  of  the 
reflex  power  of  the  cord  may  be  caused  by  opium,  by 
chloroform,  and  by  some  other  substances,  while  the 
reflex  action  is  increased  by  strychnine.  If  under  the 
skin  of  the  decapitated  frog  a  solution  of  strychnine  be 
injected,  the  cord  in  a  short  time  becomes  so  irritable 
that  a  stimulus  which  before  would  have  had  no  effect 
will  now  produce  the  most  marked  results,  a  slight  blow 
upon  the  skin  sufficing  to  throw  the  animal  into  a  con- 
vulsive state.  In  tetanus  the  same  irritable  condition  of 
the  cord  exists,  and  in  this  state  the  patient  may  be 
thrown  into  convulsions  by  the  simple  opening  and 
closing  of  a  door. 

Special  Centres  in  the  Cord. — It  is  the  practice  to  speak 
of  certain  centres  as  existing  in  the  spinal  cord;  that  is, 
of  definite  collections  of  cells  which  preside  over  definite 
functions.  Among  these  centres  the  following  have  been 
described:  Musculo-tonic,  respiratory,  cardio-accelera- 
tor,  vaso-motor,  sudorific,  cilio-spinal,  genito-spinal,  ano- 
spinal,  vesico-spinal,  trophic,  for  erection  of  the  penis, 
for  parturition,  and  others. 

Muscnlo-tonic  Centre. — This  centre  is  continually  dis- 
charging impulses  which  keep  the  muscular  system  in  a 
condition  of  slight  contraction :  this  is  called  "  muscular 
tone."  It  is  questionable  whether  this  condition  is  to  be 
attributed  to  any  special  centre  rather  than  to  the  action 
of  all  those  cells  whose  function  it  is  to  send  out  motor 
impulses. 

Respiratory  Centre. — The  principal  respiratory  centre 


NERVOUS  FUNCTIONS.  24 1 

is  in  the  medulla,  but  experiments  in  which  this  struc- 
ture has  been  destroyed  while  some  respiratory  move- 
ments persisted  demonstrate  that  to  a  certain  extent, 
doubtless  very  slight,  the  spinal  cord  controls  the  respi- 
ratory processes. 

Cardio-accclc7-ator  Centre. — The  spinal  cord  through 
the  cardiac  nerves  and  plexus  sends  impulses  to  the 
heart,  causing  it  to  beat  more  rapidly ;  that  is,  they  ac- 
celerate its  movements.  These  impulses  are  not  con- 
stantly emitted,  as  are  the  inhibitory  impulses  which 
travel  by  the  pneumogastric. 

Vaso-motor  Centre. — The  vaso-motor  centre  in  the 
cord  is  entirely  subsidiary  to  that  in  the  medulla. 

Sudorific  Centre. — The  existence  of  special  nerves  con- 
trolling the  secretion  of  sweat  seems  to  be  demonstrated. 
These  nerves  come  from  the  spinal  cord,  being  a  part  of 
the  anterior  roots. 

Cilio-spinal  Centre. — Nerve-fibres  pass  from  this  centre 
to  the  iris,  and  they  are  concerned  in  the  dilatation  of 
the  pupil.  These  fibres  come  out  from  the  cord  through 
the  anterior  roots  of  the  spinal  nerves,  from  the  fifth  cer- 
vical to  the  fifth  thoracic,  and  join  the  cervical  sympathetic. 

Genito-spinal  Centre. — The  genito-spinal  is  the  centre 
which  governs  the  emission  of  semen,  and  is  situated 
in  the  lumbar  region  of  the  cord.  Sensory  impulses 
from  the  glans  penis  reach  this  centre  through  afferent 
nerves  and  stimulate  it,  and  from  it  go  out  efferent  im- 
pulses which  cause  contraction  of  the  muscular  fibres  of 
the  vasadefcrcntia,  seminal  vesicles, and  accelerator  urinae, 
the  result  of  which  is  to  produce  an  ejection  of  semen. 

Ano-spinal  Centre. — The  act  of  defecation  is  governed 
by  the  ano-spinal  centre.  The  mucous  membrane  and 
muscular  coat  of  the  rectum  are  supplied  with  nerves 

16 


242  HUMAN  PHYSIOLOGY. 

from  the  several  plexuses  of  spinal  nerves.  Faeces  do 
not  ordinarily  pass  into  the  rectum  until  about  the  time 
of  evacuation,  when  they  are  expelled  from  the  sigmoid 
flexure  into  the  rectum.  At  this  time  the  sphincter  ani 
is  in  a  state  of  contraction,  which  is  its  usual  condition, 
kept  so  by  the  impulses  that  come  from  the  spinal  cord. 
This  contraction  keeps  the  anus  closed  even  during 
sleep,  and  it  is  entirely  independent  of  the  action  of  the 
brain ;  it  is  an  involuntary  act.  When,  however,  faeces 
enter  the  rectum,  the  nerves  of  its  mucous  membrane 
become  stimulated,  and  these  impulses  are  conveyed  by 
afferent  nerves  to  the  ano-spinal  centre  in  the  lumbar  en- 
largement of  the  cord,  and  from  this  are  reflected  im- 
pulses which,  conveyed  to  the  sphincter,  cause  its  relax- 
ation. Under  the  influence  of  similar  impulses  which 
pass  to  the  levator  ani  this  muscle  contracts  and  draws 
upward  the  edges  of  the  anus,  causing  it  to  open,  while 
at  the  same  time  the  muscular  fibres  of  the  rectum  con- 
tract and  expel  the  faeces.  If  the  stimulation  be  very 
pronounced,  the  abdominal  muscles  may  also  be  called 
into  action,  irrespective  of  the  will,  but  when  the  stimu- 
lus is  slight  they  may  only  respond  when  called  upon  by 
the  brain.  The  connection  between  the  brain  and  the 
ano-spinal  centre  is  very  close,  so  that  the  action  of  the 
latter  may  for  a  time  be  inhibited,  but  if  the  rectum  be- 
come very  much  distended  the  impulses  may  be  so  strong 
that,  despite  the  will,  defecation  will  take  place. 

Involuntary  Discharges. — In  some  forms  of  disease 
the  irritability  of  the  ano-spinal  centre  is  so  great  that 
when  the  rectum  is  only  partially  filled  defecation  takes 
place,  and  there  is  no  power  to  retard  it.  Discharges 
under  these  circumstances    are  said  to  be  involuntary. 

Involuntary  and   Unconscious  Discharges. — If  by  rea- 


NERVOUS   FUNCTIONS.  243 

son  of  disease  or  of  injury  the  middle  or  the  upper  por- 
tions of  the  cord  become  so  disorganized  as  to  cut  off 
communication  with  the  brain,  while  at  the  same  time  the 
lower  portion  is  in  normal  condition,  the  act  of  defeca- 
tion takes  place  when  the  rectum  becomes  sufficiently 
distended  to  stimulate  the  ano-spinal  centre  to  action ; 
but  there  is  no  power  to  retard  it  nor  is  there  any  con- 
sciousness of  it,  since  the  connection  with  the  brain  is 
severed.  Under  these  circumstances  the  discharges  are 
involuntary  and  unconscious.  If  the  lumbar  portion  of 
the  cord  be  the  seat  of  injury  or  of  disease  to  such  an 
extent  as  to  destroy  this  centre,  the  sphincter  is  per- 
manently relaxed,  and  the  faeces  are  discharged  as  fast 
as  they  reach  the  anus. 

Vesicospinal  Centre. — The  act  of  micturition  is  under 
the  influence  of  the  vesico-spinal  centre.  Like  the 
genito-spinal,  this  is  situated  also  in  the  lumbar  enlarge- 
ment. The  urine  formed  in  the  kidneys  passes  into  the 
ureters,  and  thence,  under  the  influence  of  the  peristaltic 
action  of  the  muscular  coat  of  the  walls  of  these  vessels, 
into  the  bladder.  This  contraction  lasts  about  one-third 
of  a  second,  and  takes  place  alternately  in  the  ureters, 
so  that  the  urine  does  not  flow  into  the  bladder  from 
both  kidneys  at  the  same  time.  It  accumulates  in  the 
bladder  until  such  time  as  it  is  voided. 

The  bladder,  like  the  rectum,  is  supplied  with  nerve- 
fibres  which  have  their  origin  in  the  vesico-spinal  centre. 
The  urine  is  retained  within  the  bladder  by  the  tonic 
contraction  of  the  sphincter  vesicas  in  the  same  manner 
as  faeces  are  retained  in  the  rectum  by  the  sphincter  ani. 
The  pressure  of  the  urine  when  the  bladder  is  full  is  only 
equal  to  i  cm.  of  mercury,  while  it  takes  a  pressure  of 
at  least  3  cm,  to  overcome  the  elasticity  of  the  sphincter. 


244  HUMAN  PHYSIOLOGY. 

When  the  bladder  is  about  to  be  emptied  a  voluntary- 
impulse  transmitted  to  the  sphincter  vesicae  causes  its 
relaxation.  At  the  same  time  the  muscular  coat  of  the 
bladder  and  the  abdominal  muscles  contract,  and  the 
urine  begins  to  flow.  The  pressure  which  is  thus  exerted 
equals  lO  cm.  of  mercury.  Although  the  starting  of  the 
act  is  voluntary,  when  once  it  has  begun  it  continues 
under  the  influence  of  the  vesico-spinal  centre  alone  until 
the  bladder  is  empty. 

Up  to  a  certain  point  the  brain  is  able  to  inhibit  the 
centre  and  postpone  the  evacuation  of  the  bladder,  but 
after  a  time,  if  too  long  delayed,  the  resistance  of  the 
sphincter  is  overcome  and  urine  will  flow.  It  is  more 
difficult  to  stop  the  act  after  it  has  cfnce  begun  than  to 
delay  its  beginning,  for  the  urine,  flowing  over  the  mucous 
membrane  of  the  urethra,  stimulates  the  vesico-spinal 
centre,  and  the  efferent  impulses  to  the  contracting  mus- 
cles are  increased. 

If  the  mucous  membrane  of  the  bladder  be  inflamed, 
as  in  cystitis,  the  stimulation  of  the  centre  may  be  so 
great  as  to  prevent  the  brain  from  inhibiting  the  evacua- 
tion, and  evacuation  may  occur  when  only  a  small  quantity 
of  urine  has  accumulated.  Or  it  may  happen  that  the 
spinal  cord  is  injured  or  is  diseased  in  the  upper  or  mid- 
dle portion,  and  thus  all  sensation  caused  by  a  full  blad- 
der may  be  abolished.  Under  these  circumstances  the 
bladder,  when  full,  will  be  emptied  by  the  reflex  action 
of  the  vesico-spinal  centre.  Or,  again,  if  the  lesion  of 
the  cord  be  such  as  to  disorganize  this  centre,  then  there 
will  be  no  reflex  action  of  the  cord,  and  the  elasticity  of 
the  tissues  about  the  neck  of  the  bladder  will  keep  the 
urine  in  that  viscus  until  it  is  overcome  by  the  disten- 
tion, when  it  will  flow  in  drops  as  fast  as  it  comes  from 


NERVOUS  FUNCTIONS.  245 

the  kidneys,  but  the  organ  will  not  empty  itself.  Inex- 
perienced persons  are  often  deceived  by  this  dribbling 
of  the  urine,  thinking  that  its  discharge  is  evidence  that 
the  bladder  is  performing  its  duty,  while  the  fact  is  that 
it  is  evidence  of  paralysis  and  retention. 

TropJiic  Centres. — It  has  already  been  seen  that  when 
nerve-fibres  are  divided  they  undergo  degeneration,  and 
that  this  is  explained  by  the  fact  that  under  these  cir- 
cumstances their  connection  with  certain  nerve-cells  is 
severed,  and  that  they  are  thus  deprived  of  the  nutri- 
tive influence  which  such  centres  exert.  Such  centres 
are  called  "trophic  centres,"  and  the  cells  of  the  anterior 
cornua  of  the  cord  and  the  ganglia  on  the  posterior  roots 
of  the  spinal  nerves  are  familiar  illustrations.  That  these 
are  true  trophic  centres  for  nerves  seems  to  be  beyond 
dispute,  but  this  is  an  entirely  different  question  from 
that  which  deals  with  trophic  nerves  as  regulating  the 
nutrition  of  tissues  other  than  nerves.  About  the  exist- 
ence of  such  nerves  there  is  considerable  doubt. 

Other  Centres. — Some  writers  describe  a  centre  for  erec- 
tion of  the  penis,  and  locate  it  in  the  lumbar  enlargement. 
The  afferent  nerves  from  the  penis  cause  this  centre  to 
send  out  efferent  impulses  by  which  the  blood-vessels  are 
dilated  and  the  muscles  are  compressed,  thus  preventing 
the  return  of  the  venous  blood  from  the  penis  and  bring- 
ing about  erection.  A  centre  for  parturition  is  also  located 
in  the  lumbar  region  of  the  cord,  above  the  centres  already 
mentioned,  under  the  influence  of  which  the  muscular  tis- 
sue of  the  uterus  contracts  at  the  proper  time  and  expels 
the  foetus.  Other  reflex  centres  are  described,  but  the  tend- 
ency to  extend  the  number  of  such  centres  seems  to  be 
beyond  what  the  actual  facts  warrant.  However,  enough 
has  been  said  to  show  the  great  importance  of  the  spinal 


246  HUMAN  PHYSIOLOGY. 

cord  as  a  nervous  centre,  independently  of  its  function  as 
a  conductor  of  nervous  impulses  to  and  from  the  brain. 

The  Brain. 

The  brain,  or  encephalon,  is  that  part  of  the  cerebro- 
spinal axis  situated  within  the  cranium  or  skull.  Its  di- 
visions are  sometimes  described  as  \h&  fore-brain,  includ- 
ing the  hemispheres,  with  the  olfactory  lobe,  the  corpora 
.striata,  and  the  optic  thalami ;  the  mid-bimin,  being  the 
corpora  quadrigemina  and  the  crura  cerebri ;  and  the 
hind-bj'aiii — that  is,  the  cerebellum,  the  pons  Varolii, 
and  the  medulla  oblongata. 

In  the  adult  male  the  brain  weighs,  on  an  average, 
141 5  grammes  avoirdupois  :  in  the  female,  1245  grammes. 
In  278  cases  of  males  in  which  the  brain  was  weighed 
the  maximum  was  1841  grammes  and  the  minimum 
963  grammes.  In  191  cases  of  females  the  maximum 
was  1586  grammes  and  the  minimum  878  grammes. 
The  brain  of  Cuvier,  the  great  naturalist,  weighed  181 5 
grammes  ;  that  of  an  idiot  weighed  65  i  grammes.  The 
brain  of  a  mulatto  not  remarkable  for  intelligence  weigh- 
ed 1927  grammes.  The  fore-brain  weighs  about  1245 
grammes  in  the  adult  male. 

The  gray  matter  of  the  brain  is  in  some  parts  on  the 
surface,  as  in  the  convolutions  of  the  cerebrum ;  in  other 
parts  it  is  deeply  situated,  as  in  the  basal  ganglia,  the 
corpora  striata,  and  the  optic  thalami ;  while  in  still  other 
parts  it  is  scattered  about  without  any  fixed  arrangement, 
as  in  the  pons  Varolii.  The  white  matter  is  made  up  of 
fibres  which  come  from  the  spinal  cord  ;  of  fibres  having 
their  origin  in  the  gray  matter,  and  which,  escaping  from 
the  skull,  go  to  their  points  of  distribution  as  the  cranial 
nerves ;  and  of  still  other  fibres  connecting  the  ganglia 
with  one  another  and  forming  commissures. 


NERVOUS  FUNCTIONS. 


247 


The  Medulla  Oblongata 
bulb,  is  a  continuation  of 
2.5  cm.  long,  2  cm.  broad, 
and  1.2  cm.  thick.  It  is 
composed  of  gray  and 
white  rnatter.  The  gray 
matter,  which  in  the  cord 
has  the  characteristic  dou- 
ble crescentic  shape,  ap- 
proaches more  and  more 
the  posterior  surface  of 
the  cord  as  the  region  of 
the  medulla  is  reached 
and  the  posterior  cornua 
become  more  and  more 
external,  the  whole  mass 
of  gray  matter  flattening 
out,  until  in  the  medulla 
it  forms  a  layer  the  outer 
portions  of  which  repre- 
sent the  posterior  horns 
and  the  middle  portions 
the  anterior.  The  poste- 
rior columns  separate  in 
the  medulla,  the  central 
canal  coming  to  the  sur- 
face posteriorly  and  end- 
ing in  the  fourth  ventricle, 
the  floor  of  which  is  the 
gray  matter  above  referred 
to,  which  is,  however,  not 
limited  to  this  site,  but  is 
present    about    the   aque- 


. — The  medulla  oblongata,  or 
the  spinal  cord,  and  is  about 


Fig.  51. — View,  from  below,  of  the  Connec- 
tion of  the  Principal  Nerves  with  the 
Brain:  I',  the  right  olfactory  tract;  II, 
the  left  optic  nerve ;  11',  the  right  optic 
tract  (the  left  tract  is  seen  passing  back 
into  /and  e,  the  internal  and  external  cor- 
pora geniculata) ;  III,  the  left  oculo-motor 
nerve;  IV,  the  trochlear;  V,V,  the  large 
roots  of  the  trifacial  nerves;  +  +,  the 
lesser  roots  (the  +  of  the  right  side  is 
placed  on  the  Gasserian  ganglion);  i,  the 
ophthalmic  ;  2,  the  superior  maxillary  ;  and 
3,  the  inferior  maxillary  divisions;  VI, 
the  left  abducens  nerve;  VII,  VIII,  the 
facial  and  auditory  nerves;  IX-XI,  the 
glosso-pharyngeal,  pneumogastric,  and 
spinal  accessory  nerves:  XII,  the  right 
hypoglossal  nerve;  C,,  the  left  suboccipi- 
tal or  first  cervical  nerve  (Nancrede). 


248  HUMAN  PHYSIOLOGY. 

duct  of  Sylvius.  From  this  gray  matter  arise  all  the 
cranial  nerves  excepting  the  olfactory  and  optic. 

The  medulla,  like  the  cord,  has  an  anterior  and  a  pos- 
terior median  fissure.  At  the  lower  part  of  the  anterior 
fissure  are  fibres  that  cross  from  side  to  side,  the  decus- 
sation of  the  anterior  pyramids.  The  posterior  fissure 
of  the  cord  widens  out  and  forms  the  fourth  ventricle. 
Some  of  the  cranial  nerves  come  out  from  the  medulla, 
and  serve  as  boundaries  to  describe  the  different  portions 
of  the  medulla.  That  portion  of  white  matter  between 
the  anterior  median  fissure  and  the  roots  of  the  hypo- 
glossal nerve  is  the  anterior  pyramid.  The  lateral  col- 
umn is  between  the  roots  of  the  hypoglossal  and  those 
of  the  glosso-pharyngeal,  the  pneumogastric,  and  the 
spinal  accessory.  At  the  upper  portion  the  olivary 
body  lies  between  the  column  and  the  pyramid.  The 
posterior  column  is  between  the  lateral  column  or  tract 
and  the  posterior  median  fissure.  It  is  composed  of 
three  smaller  columns  separated  by  shallow  grooves,  the 
most  external  being  the  funiculus  of  Rolando,  next  the 
funiculus  cuneatus,  and  the  most  internal  the  funiculus 
gracilis,  the  first  two  being  joined  in  the  upper  part  of 
the  medulla  to  form  the  restiform  body.  The  outer  por- 
tion of  the  pyramid  is  derived  from  the  direct  pyramidal 
tracts  of  the  same  side,  while  the  decussation  consists 
of  the  fibres  of  the  crossed  pyramidal  tract  of  the  lateral 
column. 

In  the  restiform  bodies  are  to  be  found,  besides  the 
funiculus  of  Rolando  and  the  funiculus  cuneatus,  fibres 
of  the  direct  cerebellar  tract  of  the  lateral  column.  These 
bodies  form  the  inferior  peduncles  of  the  cerebellum.  The 
funiculus  of  Rolando  is  the  enlarged  head  of  the  poste- 
rior cornu   of  the  cord,  and  is  therefore  gray   matter. 


NERVOUS  FUNCTIONS.  249 

The  funiculus  cuneatus  is  the  continuation  of  Burdach's 
column  of  the  cord,  and  the  funiculus  gracilis  is  the  con- 
tinuation of  GoU's  column. 

Functions  of  the  Medulla  Oblongata. —  Conduction. — 
All  the  impulses,  whether  afferent  or  efferent,  passing  be- 
tween the  brain  and  the  cord  must  pass  through  the 
medulla. 

Nerve-centres. — Experiments  have  demonstrated  that 
all  the  brain  above  the  medulla  and  all  the  spinal  cord 
may  be  removed  and  yet  life  be  maintained,  provided 
that  the  origin  of  the  phrenic  nerves  be  left  intact,  while 
if  all  these  structures  be  undisturbed  and  the  medulla  be 
broken  up  death  will  result.  The  centres  in  the  medulla 
are  both  reflex  and  automatic. 

Reflex  Centres. — One  of  the  most  important  of  these 
centres  is  that  which  presides  over  deglutition.  As  has 
already  been  seen  in  discussing  this  process,  the  first 
stage  of  the  act  is  voluntar)^  but  as  soon  as  the  food  has 
passed  into  the  pharynx  the  act  becomes  involuntary. 
The  mucous  membrane  of  the  pharynx  is  stimulated  by 
the  food,  and  the  afferent  fibres  of  the  glosso-pharyngeal 
transmit  the  impulse  to  the  medulla,  in  which  a  motor 
impulse  is  generated,  and  out  along  the  efferent  fibres 
comes  the  impulse  to  the  constrictors  of  the  pharynx. 
Centres  for  vomiting,  coughing,  sucking,  and  for  other 
movements  are  described  by  some  writers. 

Vomithii!^. — When  the  act  of  vomiting  takes  place 
there  is  first  an  inspiration ;  after  this  the  glottis  is 
closed  and  so  remains.  The  lungs  being  filled  with  air 
and  the  glottis  being  closed,  no  air  can  escape,  and  the 
diaphragm  therefore  remains  fixed  as  it  is  at  the  end  of 
an  inspiration.  The  abdominal  muscles  then  compress 
the  stomach  against  the  fixed  diaphragm,  and  the  cir- 


250  HUMAN  PHYSIOLOGY. 

cular  fibres  at  the  cardiac  orifice  of  the  stomach  (the 
cardiac  sphincter)  being  relaxed,  this  orifice  opens,  and, 
as  at  the  same  time  the  pyloric  orifice  is  closed,  the 
stomach  is  emptied  of  its  contents  into  the  oesophagus. 
The  muscular  coat  of  this  tube  by  reversed  peristalsis 
carries  the  material  to  the  pharynx  and  the  mouth,  where 
it  is  expelled.  Whether  the  muscular  coat  of  the  stom- 
ach takes  any  part  in  the  evacuation  is  questioned  by 
some  authors,  on  the  ground  that  the  stomach  may  be 
replaced  by  a  bag  whose  contents  will  be  expelled  by  the 
contractions  of  the  abdominal  muscles  alone;  but  the 
probability  is  that  the  gastric  muscular  fibres  also  con- 
tract. Whether  these  contribute  much  toward  expelling 
the  contents  in  the  adult  is  not  determined,  but  they  are 
probably  the  only  agency  in  the  infant. 

The  act  of  vomiting  is  a  reflex  one,  in  which  the  fibres 
of  the  pneumogastric  serve  as  afferent  fibres,  the  impulses 
stimulating  the  centre  in  the  medulla  from  which  em- 
anate motor  impulses  to  the  respiratory  and  other 
muscles  concerned  in  the  act.  If  the  act  of  vom- 
iting 'be  brought  on  by  stimulating  the  pharynx  with 
a  feather  or  with  a  finger,  the  glosso-pharyngeal  is  the 
carrier  of  the  afferent  impulses.  Afferent  impulses  pro- 
ducing vomiting  may  also  come  from  other  organs,  such 
as  the  kidneys,  or  the  testicles  when  injured. 

Central  Vomiting. — In  central  vomiting  the  centre  is 
stimulated  by  impulses  which  come  from  the  brain. 

Riiniination. — The  power  to  ruminate,  by  virtue  of 
which  animals  chew  the  cud,  is  possessed  by  some 
human  individuals,  who  can  regurgitate  the  food  when- 
ever they  feel  so  disposed,  and  chew  it  again. 

Automatic  Centres. — Besides  reflex  centres,  which  re- 
quire a  stimulus  from  without  to  bring  them  into  action, 


NERVOUS  FUNCTIONS.  25  I 

the  medulla  possesses  automatic  centres  which  generate 
and  emit  impulses  independently  of  stimuli  from  without. 

Respiratory  Centre. — This  centre  is  situated  in  the 
floor  of  the  fourth  ventricle,  and  when  injured  respira- 
tion ceases  immediately.  Some  authorities  place  it 
among  the  reflex  centres.  As  will  be  seen,  it  may  be 
excited  reflexly,  but  there  are  reasons  for  believing  it 
to  possess  automatic  powers  as  well.  If  the  spinal 
cord  be  divided  below  the  medulla,  although  the  respi- 
ratory movements  of  the  thorax  cease,  those  of  the  nose 
and  larynx  continue.  Under  these  circumstances  no 
afferent  impulses  can  be  transmitted  through  the  spinal 
nerves,  and  the  only  channel  is  the  cranial  nerves ;  but 
if,  while  the  medulla  and  cord  are  left  undisturbed,  the 
cranial  nerves  be  cut,  respiration  continues.  These  two 
series  of  experiments  show  that  respiration  will  continue 
without  the  reception  of  any  impulses  from  without; 
that  is,  automatically. 

The  principal  nerves  that  transmit  the  impulses  pro- 
ducing the  respiratory  movements  are  the  intercostals, 
and  the  phrenics  to  the  diaphragm.  The  respiratory 
centre  is  double,  so  that  one  side  may  act  after  the  other 
is  divided.  Division  of  one  phrenic  paralyzes  only  the 
side  of  the  diaphragm  to  which  it  is  distributed.  The 
respiratory  centre  may  also  be  excited  reflexly.  The 
afferent  fibres  under  these  circumstances  are  those  of 
the  pneumogastric. 

Resistance  Theory  of  Respiration. — Tf  a  pair  of  bellows 
be  connected  with  the  trachea  of  an  animal,  and  air 
thereby  be  supplied  to  its  lungs,  there  will  be  no  respi- 
ratory movements  made  by  the  animal  itself,  but  if  the 
supply  of  air  be  discontinued,  after  a  time  respiratory 
efforts  will  be  made,  and  they  will  be  rhythmic  in  cha- 


252  HUMAN  PHYSIOLOGY. 

racter.  The  explanation  of  this  fact  is  by  no  means  cer- 
tain, but  the  following  theory  has  been  advanced : 

In  the  respiratory  centre  of  the  medulla  certain  chem- 
ical changes  are  constantly  taking  place,  the  result  of 
which  is  the  production  of  a  substance  which  is  a  stim- 
ulant to  the  nerve-cells  composing  this  centre,  and  these 
cells  when  stimulated  send  out  impulses  to  the  inspira- 
tory muscles,  causing  them  to  contract,  thus  producing 
an  inspiration.  This  substance  is  destroyed  by  oxygen 
when  the  amount  in  the  blood  reaches  a  certain  point. 
This  point  is  reached  when  air  is  supplied  by  the  bellows 
in  the  experiment  above  referred  to ;  but  the  blood, 
which,  under  normal  conditions,  is  supplied  to  the  me- 
dulla, is  not  rich  enough  in  oxygen  to  completely  destroy 
this  substance,  and  therefore  it  accumulates  and  stimu- 
'lates  the  nerve-cells,  bringing  about  the  inspiratory  act. 
When  the  blood  is  venous  this  substance  accumulates 
more  rapidly  and  the  respiratory  acts  are  more  frequent. 

The  rhythmic  character  of  respiration  is  accounted  for 
by  supposing  that  the  nervous  energy  from  the  cells, 
passing  over  the  respiratory  nerves  to  the  muscles,  meets 
with  such  resistance  that  the  discharge  can  only  take  place 
after  the  impulses  have  accumulated  to  a  certain  extent  in 
the  centre,  and  that  when  this  occurs  the  discharge  takes 
place  and  the  inspiration  follows ;  then  there  is  a  period 
of  rest,  during  which  time  the  accumulation  is  again 
taking  place,  and  when  the  proper  point  is  reached 
another  discharge  occurs,  to  be  followed  by  the  in- 
spiratory act.  It  is  of  course  to  be  understood  that 
this  theory  is  provisional  only.  Whether  such  a  sub- 
stance exists  or  not  is  undetermined. 

Asphyxia. — This  condition  may  be  appropriately  de- 
scribed at  this  place,  now  that  the  relation  between  the 


NERVOUS  FUNCTIONS.  253 

lungs  and  the  nervous  system  is  understood.  The  term 
hterally  means  "pulselessness,"  and  is  especially  applica- 
ble to  the  fourth  stage.  If  by  any  means  the  supply  of 
air  to  an  animal  be  prevented,  death  results  within  a  very 
few  minutes  by  asphyxia.  The  animal  before  the  fatal 
termination  arrives  passes  through  four  stages — namely, 
(i)  dyspnoea;  (2)  convulsion;  (3)  exhaustion;  and  (4) 
inspiratory  spasm. 

(i)  Dyspncna. — As  soon  as  the  air  is  cut  off  the  blood 
becomes  more  and  more  venous ;  that  is,  loses  more  and 
more  of  its  oxygen.  The  respiratory  centre  becomes 
more  stimulated,  and  efferent  impulses  call  into  play 
the  extraordinary  muscles  of  respiration — the  sterno- 
mastoid,  the  serratus  magnus,  the  pectoralis,  and  the 
trapezius.  This  dyspnoeic  stage,  or  stage  of  difficult 
or  labored  breathing,  continues  for  about  one  minute. 

(2)  Convulsion. — In  the  second  stage  the  movements 
of  inspiration  become  feebler,  while  those  of  expiration 
become  stronger,  and  at  length  the  muscles  of  the  whole 
body  are  thrown  into  a  state  of  convulsion.  This  stage 
is  very  brief. 

(3)  Exhaustion. — The  expiratory  muscles  being  ex- 
hausted, the  animal  becomes  quiescent,  only  a  few  slight 
attempts  at  inspiration  being  perceptible.  After  a  time 
these  become  deeper,  but  only  occur  at  comparatively 
long  intervals.  The  third  stage  is  longer  than  the  first 
or  the  second. 

(4)  Inspiratory  Spasm. — The  intervals  between  the 
inspirations  have  in  this  stage  greatly  increased,  and 
apparently  ceased,  but  they  recur  occasionally.  The 
pupils  are  dilated  and  the  pulse  is  less  and  less  percept- 
ible ;  finally  a  last  inspiration  occurs  and  the  animal  is 
dead. 


254  HUMAN  PHYSIOLOGY. 

Cardio-inhibitory  Centre. — In  the  cardio-inhibitory 
centre  are  generated  those  impulses  which,  travelling 
to  the  heart  by  the  pneumogastric  nerve,  inhibit  or 
restrain  the  action  of  that  organ.  This  subject  will  be 
more  fully  discussed  in  connection  with  the  functions 
of  the  pneumogastric  nerve.  The  accelerator  nerves 
of  the  heart  have  their  origin  in  the  spinal  cord,  and 
are  distributed  to  that  organ  through  the  sympathetic 
ganglia.  Whether  they  have  any  origin  in  the  medulla 
is  doubtful.  They  are  antagonistic  to  the  pneumogas- 
tric, and  carry  impulses  to  the  heart  which  hasten  its 
action. 

Vaso-inotor  Centre. — The  exact  location  of  the  vaso- 
motor centre  in  the  medulla  of  man  is  not  definitely 
settled,  but  it  is  probably  in  the  floor  of  the  fourth  ven- 
tricle. From  this  centre  go  impulses  over  the  vaso- 
constrictor nerves,  which  impulses  tend  to  constrict  the 
arteries ;  hence  it  has  been  suggested  that  it  should  be 
called  the  "  vaso-constrictor  centre." 

Tlie  muscular  coat  of  the  arteries  is  innervated  first  by 
fibres  which  arise  in  ganglion-cells  situated  either  in  the 
walls  of  the  vessels  or  very  near  them.  These  ganglia 
are  called  "  intrinsic  ganglia,"  and  the  nerves  coming 
from  them  are  called  "  intrinsic  nerves."  They  are  con- 
stantly generating  and  emitting  impulses  which  keep  the 
muscular  fibres  in  a  state  of  slight  but  generally  constant 
contraction,  called  "  muscular  tone."  The  second  source 
of  innervation  of  the  muscular  coat  of  the  arteries  is  the 
vaso-constrictor  nerves  just  described.  These  nerves 
are  spoken  of  as  "  extrinsic,"  and  the  impulses  which 
they  transmit  cause  the  vessels  to  be  more  constricted 
than  they  would  be  by  the  impulses  coming  from 
the  intrinsic  ganglia.     The  vaso-constrictor  fibres  come 


NERVOUS  FUNCTIONS.  255 

from  the  sympathetic,  but  their  real  origin  is  in  the  me- 
dulla, from  which  they  pass  down  the  cord,  and  emerge 
as  constituent  parts  of  the  anterior  roots  of  some  of  the 
spinal  nerves,  joining  the  sympathetic  system  subse- 
quently. 

Although  the  vaso-motor  centre  is  here  classified  among 
the  automatic  centres,  it  may  also  be  excited  reflexly. 
The  sensory  nerves  of  the  body  are  for  the  most  part 
connected  with  it,  and  when  severe  pain  is  experienced 
the  centre  may  be  stimulated,  and  as  a  result  the  im- 
pulses generated  may  constrict  the  arteries,  and  thus  by 
increasing  the  resistance  of  the  blood-current  increase 
arterial  pressure. 

Depressor  Nerve-fibres. — Between  the  heart  and  the 
medulla  are  nerve-fibres  which  carry  impulses  from  the 
heart  to  the  vaso-motor  nerve-centre,  which  impulses 
inhibit  the  centre,  and  thus  diminish  the  impulses  to 
the  muscular  coat  of  the  arteries,  thereby  causing  the 
arteries  to  dilate  and  reducing  arterial  pressure.  In  the 
rabbit  these  fibres  are  together  and  form  the  depressor 
nerve,  but  in  most  animals  they  are  joined  with  the 
fibres  of  the  pneumogastric.  By  means  of  these  fibres 
the  nerve-centre  can  be  inhibited  and  arterial  pressure 
be  lessened,  thus  reducing  the  work  of  the  heart. 

Pons  Varolii. — The  pons  Varolii  (tuber  annulare  or 
mesocephalon)  is  situated  just  above  the  medulla,  and  is 
made  up  of  three  sets  of  fibres  and  of  some  gray  matter. 
The  first  set  is  composed  of  superficial  transverse  fibres 
which  cross  the  upper  part  of  the  medulla  and  connect 
the  two  hemispheres  of  the  cerebellum,  forming  at  the 
sides  the  crura  cerebelli  or  middle  peduncles.  The 
.second  set  is  made  up  of  longitudinal  fibres  which  come 
from  the  pyramids  of  the  medulla  and  pass  on  to  help 


256  HUMAN  PHYSIOLOGY. 

form  the  crura  cerebri.  The  third  set  is  also  transverse 
and  is  deeply  situated,  connecting  the  middle  peduncles 
of  the  cerebellum.  Among  its  fibres  are  collections  of 
gray  matter. 

Fimctions  of  the  Pons  Varolii. — The  anatomical  rela- 
tions of  the  pons  show  that  it  must  serve  as  a  conductor 
of  impulses  both  to  and  from  the  centres  above.  As  to 
the  function  of  its  gray  matter  comparatively  little  is 
known,  save  that  from  a  portion  of  it  some  of  the 
cranial  nerves  arise.  If  it  be  stimulated  or  divided, 
pain  and  spasms  are  produced.  When  a  lesion  is  situ- 
ated in  the  lower  half  of  the  pons,  there  result  facial 
paralysis  on  the  same  side  as  the  lesion,  and  motor  and 
sensory  paralysis  of  the  opposite  side  of  the  body.  This 
is  called  alternate  paralysis.  If  the  lesion  be  in  the  upper 
half  of  the  pons,  the  facial  paralysis  and  that  of  the  body 
are  on  the  same  side.  When  the  pons  is  suddenly  and 
extensively  injured,  a  condition  of  hyperpyrexia  is  often 
produced,  the  temperature  rising  rapidly  within  an  hour- 
This  is  probably  due  to  the  influence  of  the  gray  matter 
in  the  floor  of  the  fourth  ventricle,  or  possibly  to  the  in- 
volvement of  some  special  heat-regulating  centre. 

Cerebellum. — The  cerebellum  is  composed  externally 
of  gray  matter,  which  also  penetrates  into  the  substance 
of  the  organ,  forming  with  the  white  matter  the  lamincs. 
In  the  central  part  of  the  cerebellum  is  white  matter  in 
which  is  imbedded  a  collection  of  gray  matter,  the  corpus 
dentatiini.  The  cerebellum  is  connected  with  the  rest 
of  the  encephalon  by  the  superior,  the  middle,  and  the 
inferior  peduncles.  The  superior  peduncles  (^processus  e 
cerebello  ad  testes)  connect  the  cerebellum  with  the  cere- 
brum ;  the  middle  peduncles  [cmra  cerebelli)  connect 
the    two    cerebellar    hemispheres;    the    inferior   {pro- 


NERVOUS  FUNCTIONS.  257 

ccss2(s  ad  nicdiillani)  connect  the  cerebellum  and  medulla 
oblongata. 

The  gray  matter,  as  has  been  said,  is  upon  the  sur- 
face and  in  the  interior:  that  upon  the  surface,  called 
the  "  cortex,"  is  made  up  of  two  layers — an  external 
gray,  consisting  of  neuroglia,  fibres,  and  cells,  and  an 
internal  rust-colored  layer.  In  the  gray  are  peculiar 
cells,  the  corpuscles  of  Purkinje,  which  are  flask-shaped, 
and  which  give  off  from  the  side  toward  the  internal 
layer  processes  that  terminate  in  axis-cylinders  of 
medullated  nerve-fibres.  From  the  other  side  pass  off 
processes  which  branch  in  the  external  layer,  some  of 
them  at  least  joining  with  the  cells  in  this  layer.  The 
gray  matter  in  the  interior  is  the  corpus  dentatum  and 
the  "  roof-nuclei  "  of  Stilling. 

Functions  of  the  Cerebellum. — If  the  surface  of  the 
cerebellum  be  irritated,  no  muscular  movements  are 
produced  nor  is  there  any  evidence  of  sensation  ;  if, 
however,  the  irritation  be  applied  near  the  medulla  or 
inferior  peduncles,  both  pain  and  muscular  contraction 
result.  If  the  cerebellum  be  removed  wholly  or  par- 
tially, sensation  is  not  diminished  in  the  part  of  the 
body  below,  nor  is  there  any  impairment  of  the  power 
of  producing  muscular  movements,  nor  of  the  special 
senses,  nor  of  the  intelligence ;  but  there  is  a  marked 
want  of  harmony  in  the  muscular  movements,  a  lack  of 
co-ordination.  Attention  has  already  been  called  to  the 
fact  that  even  the  simplest  movements  that  are  made 
require  the  harmonious  action  of  different  muscles,  and 
when  these  movements  are  more  complex  they  require 
different  sets  of  muscles.  If  these  movements  do  not 
occur  at  just  the  right  time  and  are  not  produced  in  the 
right  manner,  the  result  is  disorder  instead  of  harmony; 
17 


258  HUMAN  PHYSIOLOGY. 

or,  as  it  is  expressed,  there  is  a  want  of  co-ordination. 
This  is  the  effect  of  removing  the  cerebellum.  Thus, 
if  the  cerebellum  of  the  pigeon  be  removed,  and  an 
attempt  be  then  made  by  it  to  fly,  it  is  unsuccessful,  for 
this  act  requires  the  consentaneous  action  of  both  wings, 
which  action  is  absent.  In  walking  the  bird  reels  like 
a  person  intoxicated,  and  cannot  go  to  the  spot  for 
which  it  apparently  set  out.  It  should  be  borne  in 
mind  that  there  is  no  paralysis  either  of  motion  or  of 
sensation  in  this  condition,  but  the  voluntary  movements 
which  originate  in  the  cerebrum,  and  which  are  in  the 
normal  condition  co-ordinated  by  the  cerebellum,  pass 
to  the  muscles  without  this  regulating  influence,  and  the 
result  is  a  series  of  disordered  movements. 

It  is  interesting  to  know  that  in  animals  that  produce 
complex  movements  the  cerebellum  is  considerably  de- 
veloped, while  in  those  animals  whose  movements  are 
simple,  such  as  the  frog,  this  organ  is  exceedingly  small. 

Cerebrum. — The  cerebrum,  which  in  man  makes  up 
about  four-fifths  of  the  encephalon,  is  divided  into  two 
hemispheres  which  are  separated  by  the  great  longitu- 
dinal fissure  (Fig.  52),  but  are  connected  by  a  white 
commissure,  the  corpus  callositni  (Fig.  54).  The  surface 
presents  depressions,  called  "  fissures  "  and  "  sulci,"  and 
prominences,  termed  "  convolutions  "  or  "  gyri."  The 
external  portion  of  the  hemispheres  is  gray  nervous 
matter  about  3  mm.  in  thickness,  beneath  which  is  white 
matter.  The  fissures  are  not  numerous,  but  are  quite 
constant ;  they  are  folds  of  the  brain-matter  both  gray 
and  white.  The  sulci  are  depressions  of  the  gray  matter 
alone  ;  they  are  very  numerous  and  inconstant.  As  gray 
matter  is  present  on  both  sides  of  the  fissures  and  sulci, 
this    arrangement  permits  of  a  larger  amount  of  gray 


NERVOUS  FUNCTIONS. 


259 


matter  than  could  exist  were  it  only  upon  the  surface  of 
the  convolutions.  In  a  brain,  therefore,  where  the  sulci 
are  deep  and  numerous  the  amount  of  ^^ray  matter 
exceeds  that  in  a  brain  where  they  are  more  shallow 
and  less  abundant.  This  gray  matter  is  called  the 
"  cortical  substance." 

Fissures  of  the  Cerebriun.—i:\\Q  fissures  serve  as  land- 


Fig.  52. — View  of  the  Brain  from  above:  A,  anterior  central  or  a.scending  frontal  con- 
volution; ZJ,  posterior  central  or  ascending  parietal  convolution;  C,  central  fissure, 
or  fissure  of  Rolando;  cm,  calloso-marginal  sulcus  ;  F,  frontal  lobe;  /",,  upper,  F^, 
middle,  F^,  lower  frontal  convolution  ;  /", ,  superior  frontal  sulcus;  f^,  inferior  frontal 
sulcus  ;  /"j,  vertical  fissure  (sulcus  prscccntralis) ;  ifi,  interparietal  sulcus  ;  O,  occipital 
lobe;  <7,  sulcus  occipitalis  transversus  ;  C,,  first  occipital  convolution;  (?,,  second 
occipital  convolution  ;  P,  parietal  lobe  ;  po,  parieto-occipital  fissure  ;  /", ,  upper  or 
pfAtero-parictal  lobule;  P^,  lower  parietal  lobule,  constituted  by  /',,  gyrus  supra- 
marginalis;  P^ ,  gyrus  angularis  ;  5,,  end  of  the  horizontal  branch  of  the  fissura 
Sylvii  ;  /,,  upper  temporal  fissure. 


marks  in  the  description  of  the  different  parts  of  the 
hemispheres.      Besides   the    great    longitudinal    fissure, 


26o 


HUMAN  PHYSIOLOGY. 


there  are  (i)  the  fissure  of  Sylvius;  (2)  that  of  Rolando; 
and  (3)  the  parieto-occipital  fissure  (Fig.  53).  These 
fissures  divide  each  hemisphere  into  five  lobes. 

(i)  The  fissuj'e  of  Sylvius  is,  next  to  the  great  longi- 
tudinal fissure,  the  most  important.  It  is  found  in  all 
animals  whose   brains    have  any  fissures.     It  exists  in 


Fig.  53. — Outer  Surface  of  the  Left  Hemisphere:  A,  anterior  central  or  ascending 
frontal  convolution  ;  B,  posterior  central  or  ascending  parietal  convolution;  c,  sulcus 
centralis  or  fissure  of  Rolando  :  cm,  termination  of  the  calloso-marginal  fissure ;  F, 
frontal  lobe  ;  F.^,  superior,  F„,  middle,  and  F^,  inferior  frontal  convolution  ;  f-^,  supe- 
rior, and  yj,  inferior  frontal  sulcus  ;  f^,  sulcus  prsecentralis  :  ?/*,  sulcus  intraparietalis  ; 
O,  occipital  lobe;  O^,  first,  O^,  second.  O^,  third  occipital  convolutions;  o^,  sulcus 
occipitalis  transversus  ;  o^,  sulcus  occipitalis  longitudinalis  inferior;  P,  parietal  lobe; 
po,  parieto-occipital  fissure  ;  P^,  superior  parietal  or  postero-parietal  lobule;  Pn,  in- 
ferior parietal  lobule — viz.  P^,  gyrus  supramarginalis  ;  P^' ,  gyrus  angularis ;  5,  fis- 
sure of  Sylvius  :  S\  horizontal,  S" ,  ascending  ramus  of  the  same  ;  T,  temporo-sphe- 
noidal  lobe;  7",,  first,  T^,  second,  T^,  third  temporo-sphenoidal  convolutions;  ^i, 
first,  /„,  second  temporo-sphenoidal  fissures. 


the  human  brain  in  the  third  month  of  intra-uterine  life. 
It  commences  at  the  base  of  the  brain,  and  runs  outward, 
backward,  and  upward,  giving  off  a  short  anterior  branch 
or  limb.     The  continuation  of  the  fissure  backward  from 


NERVOUS  FUNCTIONS. 


261 


where  this  branch  is  given  off  is  called  the  "  posterior 
branch  "  or  horizontal  limb,  which  ends  in  the  parietal 
lobe.  The  fissure  of  Sylvius  is  the  boundary  between 
the  frontal  and  parietal  lobes  on  the  one  hand  and  the 
temporo-sphenoidal  on  the  other.  At  the  middle  and 
anterior  part  of  this  fissure,  deeply  situated,  is  the  island 
of  Reil,  or  insula,  or  central  lobe  (Fig.  53). 


Fig.  54.— Inner  Surface  of  Right  Hemisphere:  A,  ascending  frontal;  B,  ascending 
parietal  convolution  ;  r,  terminal  portion  of  the  sulcus  centralis,  or  fissure  of  Ro- 
lando;  CC.  corpus  callosum,  longitudinally  divided;  Cf,  collateral  or  occipito-tem- 
poral  fissure  (Ecker) ;  cm,  sulcus  calloso-marginalis  ;  D,  gyrus  descendens  ;  F^,  me- 
dian aspect  of  the  first  frontal  convolution  ;  Gf,  gyrus  fornicatus ;  H,  gyrus  hip- 
pocampi ;  h,  sulcus  hippocampi,  or  dentate  fissure  ;  O,  sulcus  occipitalis  transversus  ; 
oc,  calcarine  fissure ;  oc' ,  superior,  oc" ,  inferior  ramus  of  the  same  ;  0«,  cuneus :  po, 
pa'rieto-occipital  fissure;  P,",  precuneus;  7^,  gyrus  occipito-temporalis  lateralis 
(lobulus  fusiformis);  Ti,  gyrus  occipito-temporalis  medialis  (lohulus  lingualis);  U, 
uncinate  gyrus. 

(2)  The  fissure  of  Rolando  starts  near  the  median  line, 
and  runs  downward  and  forward  nearly  to  the  fissure  of 
Sylvius  (Fig.  53).  It  is  the  boundary  between  the  frontal 
and  parietal  lobes. 

(3)  The  parieto-occipital  fissure  is  about  halfway  be- 
tween the  fi.ssure  of  Rolando  and  the  posterior  extremity 
of  the  brain,  and  is  the  boundary  between  the  parietal 
and  occipital  lobes  (Fig.  54). 


262  HUMAN  PHYSIOLOGY. 

Lobes  of  the  Cerebrum. — The  lobes  of  the  cerebrum 
are  (i)  the  frontal,  (2)  the  parietal,  (3)  the  occipital,  (4) 

globulus  paracentralis. 


Fig.  55. — Lateral  View  of  the  Brain  (combined  from  Ecker) :  gyri  and  lobuli  marked 
with  antique  type,  the  sulci  and  fissures  with  italic  type. 

the  temporo-sphenoidal,  and  (5)  the  central,  or  island 
of  Reil  (Figs.  53  and  55). 

(i)  The  frontal  lobe  is  above  the  fissure  of  Sylvius  and 
in  front  of  the  fissure  of  Rolando.  It  is  divided  into 
four  convolutions  by  three  sulci,  or  fissures  as  they  are 
sometimes  called.  The  praecentral  fissure  or  sulcus  is 
in  front  of  the  fissure  of  Rolando,  and  the  convolution 
between  the  two  is  the  ascending  frontal.  From  the 
upper  extremity  of  this  sulcus  the  superior  frontal  sulcus 
runs  downward  and  forward  between  the  superior  and 
middle  frontal  convolutions,  while  from  the  lower  ex- 
tremity runs  off  the  inferior  frontal  sulcus,  separating 


NERVOUS  FUNCTIONS.  263 

the  middle  and  inferior  frontal  convolutions.  Thus  the 
frontal  lobe  is  divided  into  the  ascending,  superior,  mid- 
dle, and  inferior  frontal  convolutions. 

'(2)  TJie  parietal  lobe  is  behind  the  frontal  and  in  front 
of  the  occipital  lobe,  the  fissure  of  Rolando  being  its 
anterior,  and  the  parieto-occipital  fissure  its  posterior, 
boundary.  Its  inferior  boundary  is  the  fissure  of  Sylvius 
and  the  imaginary  continuation  of  it  to  the  superior  oc- 
cipital sulcus.  It  has  two  sulci,  the  intraparietal  and  the 
post-central,  and  three  convolutions,  the  ascending,  su- 
perior, and  inferior  parietal. 

(3)  The  occipital  lobe  is  posterior  to  the  parietal,  and 
has  two  sulci,  the  superior  and  middle,  and  three  convo- 
lutions, the  superior,  middle,  and  inferior  occipital,  the 
latter  being  subdivided  into  the  supramarginal  and  the 
angular. 

(4)  The  Temporo-sphenoidal  Lobe. — The  fissure  of  Syl- 
vius forms  the  anterior  and  superior  boundaries  of  this 
lobe,  while  its  posterior  boundary  is  the  imaginary  con- 
tinuation of  the  occipito-parietal  fissure.  It  presents  two 
sulci,  the  superior  tempero-sphenoidal  or  parallel,  and 
the  middle  temporo-sphenoidal.  Its  convolutions  are 
three,  the  superior,  middle,  and  inferior  temporo-sphe- 
noidal. 

(5)  The  central  lobe,  or  island  of  Reil,  is  situated  at  the 
base  of  the  brain,  in  the  fissure  of  Sylvius.  It  consists 
of  six  convolutions,  the  gyri  operti. 

Crura  cerebri,  also  called  the  "  peduncles  of  the  cere- 
brum," are  made  up  of  white  matter,  nerves  which  are 
continuous  with  those  already  studied  in  the  medulla 
and  pons,  together  with  nerves  from  the  cerebellum,  the 
superior  peduncles.  Between  the  superficial  fibres  of  the 
crura,  the  crusta,  and  the  deeper  ones,  the  tegmentum,  is 


264  HUMAN  PHYSIOLOGY. 

the  locus  niger,  a  collection  of  gray  matter.  The  fibres 
of  the  crura  on  their  way  upward  to  the  gray  matter  of 
the  hemispheres  pass  through  the  corpora  striata  and  the 
optic  thalami. 

Basal  Ganglia. — At  the  base  of  the  hemisphere  are 
certain  bodies,  the  basal  ganglia,  which  are  the  corpora 
striata,  the  optic  thalami,  the  tubercula  quadrigemina  or 
corpora  quadrigemina,  the  corpora  geniculata,  and  the 
locus  niger. 

Corpora  striata,  with  the  optic  thalami,  are  called  the 
"  cerebral  ganglia."  The  corpora  striata  present  a  striped 
appearance,  which  is  due  to  a  mixture  of  gray  and  white 
matter,  the  latter  being  bundles  of  fibres  which  have 
come  from  below  and  within.  Although  at  the  lowest 
part  each  corpus  striatum  is  a  single  body,  at  the  upper 
part  it  is  divided  into  two  portions  called  the  "  caudate 
nucleus "  and  "  lenticular  nucleus."  The  lenticular 
nucleus,  the  more  posterior,  is  separated  from  the  optic 
thalamus  by  white  matter,  the  internal  capsule,  which  is 
the  continuation  of  the  crus  cerebri.  Outside  the  len- 
ticular nucleus  is  white  matter,  the  external  capsule, 
beyond  which  is  a  layer  of  gray  matter,  the  claustrum, 
and  external  to  all  these  structures  is  the  "  island  of 
Rail."  The  cortical  substance  is  at  this  point  very  near 
the  gray  matter  of  the  basal  ganglia. 

Optic  Thalami. — These  bodies  are  behind  and  between 
the  corpora  striata.  The  internal  portion  is  gray  matter, 
and  the  external  white. 

Tubercula  or  corpora  quadrigemina  are  sometimes 
spoken  of  as  the  "  optic  lobes."  They  are  four  in  num- 
ber, as  their  name  indicates,  the  anterior  pair  being  the 
nates,  the  posterior  the  testes.  In  fishes  and  birds  there 
are  but  two  of  these  bodies  which  are  known  as  the  optic 


NERVOUS  FUNCTIONS.  265 

lobes.  The  processus  ad  testes,  superior  peduncle  of 
the  cerebellum,  connects  the  latter  structure  with  the 
testes.  Its  fibres  pass  through  the  tegmentum  to  the 
optic  thalami. 

Microscopical  Structure  of  Hemispheres. — Gray 
Matter. — The  gray  matter  on  the  external  surface  of  the 
cerebrum,  forming  the  cortex,  is  divisible  into  five  layers. 
The  first  or  most  superficial  layer  consists  of  neuroglia,  a 
few  small  ganglion-cells,  and  a  nerve-fibre  network  ;  the 
second  is  made  up  of  small  pyramidal  nerve-cells  having 
a  diameter  of  about  10  mmm. ;  the  third  is  similar  to  the 
second,  except  that  the  cells  are  larger,  their  diameter 
being  from  25  to  40  mmm.,  and  it  is  the  broadest  of 
all  the  layers.  The  fourth  layer  consists  of  small,  trian- 
gular or  elongated  cells,  and  the  fifth  of  spindle-shaped 
cells.  The  pyramidal  cell  or  nerve-corpuscle  above  men- 
tioned is  regarded  as  the  most  important  of  all  the  struc- 
tures in  the  gray  matter  of  the  cortex.  These  cells  pos- 
sess no  cell-wall ;  they  have  nuclei  and  give  off  pro- 
cesses. One  of  these  processes  is  branched  and  is 
termed  the  process  of  the  apex ;  its  direction  is  toward 
the  surface,  and  it  is  continuous  with  the  nerve-fibre 
network  in  the  first  layer.  Another  process,  the  process 
of  the  centre  of  the  base,  is  opposite  that  of  the  apex;  it 
does  not  branch,  and  is  the  axis-cylinder  process.  This 
process  receives  a  medullary  sheath  and  forms  a  nerve- 
fibre  which  passes  into  the  white  matter  of  the  brain. 
From  the  sides  of  these  pyramidal  cells  are  given  off 
other  processes,  the  processes  of  the  basal  angle,  which 
terminate  in  a  network  of  fine  nerve-fibres. 

The  above  description  applies  in  general  to  the  whole 
cortical  substance,  but  the  structure  differs  in  some 
particulars  in  special  parts,  as,  for  instance,  at  the  pos- 


266  HUMAN  PHYSIOLOGY. 

terior  portion  of  the  occipital  lobe,  where  there  are  eight 
layers. 

The  gray  matter  of  the  corpora  striata  consists  of  large 
and  small  multipolar  nerve-cells.  Some  of  the  white 
matter  of  the  corpora  striata  is  probably  nerve-fibres 
originating  in  these  cells.  The  gray  matter  of  the  optic 
thalami  is  composed  of  multipolar  and  spindle-shaped 
nerve-cells.  The  testes  consist  almost  entirely  of  gray 
matter  covered  by  a  small  amount  of  white.  The  nerve- 
cells  are  small  and  multipolar.  The  structure  of  the 
nates  differs  somewhat  from  that  of  the  testes,  the  gray 
matter  being  in  strata;  besides  which  there  is  white 
matter.  The  cells  are  similar  to  those  in  the  testes. 
The  gray  matter  of  the  corpora  geniculata  is  continuous 
with  that  of  the  optic  thalami.  In  some  of  the  cells  of 
one  of  these  bodies,  the  corpus  geniculatum  externum, 
there  is  pigment  which  gives  them  a  dark  color.  The 
locus  niger,  a  collection  of  gray  matter  in  the  crura 
cerebri,  contains  also  pigmented  multipolar  cells.  From 
its  dark  color,  due  to  the  pigment,  it  has  received  its 
name. 

When  the  brain  is  developed  during  foetal  life  the  de- 
velopment takes  place  about  a  tube,  which  remains  in 
the  adult  as  the  aqueduct  of  Sylvius  and  the  third  and 
fourth  ventricles.  This  tube  is  continuous  with  the  central 
canal  of  the  spinal  cord,  and  is  lined  with  gray  matter,  so 
that  gray  matter  exists  in  the  aqueduct  of  Sylvius,  on 
the  inner  wall  of  the  optic  thalami,  where  it  forms  the 
gray  commissure  of  the  third  ventricle,  on  the  floor  of 
the  third  ventricle,  and  in  the  tegmentum  of  the  crus. 
It  forms  the  posterior  perforated  space,  lamina  cinerea, 
tuber  cinereum,  and  infundibulum.  The  gray  matter 
which  has  been  mentioned  as   lining  the  aqueduct  of 


NERVOUS  FUNCTIONS.  267 

Sylvius  contains  multipolar  cells  which  are  not  isolated, 
but  form  collections  called  "  nuclei ;"  from  one  of  these 
originates  the  third,  and  from  another  the  fourth,  cranial 
nerve.  From  this  description  it  will  be  seen  that  the 
gray  matter  of  the  cerebrum  is  arranged  in  three  groups  : 
(i)  that  which  forms  the  cortex ;  (2)  that  which  is  found 
in  the  basal  ganglia;  and  (3)  that  which  is  in  the  central 
portions. 

White  Matter. — The  white  matter  of  the  cerebrum, 
consisting  of  medullated  nerve-fibres,  may  be  divided 
into  three  groups  : 

I.  Those  fibres  that  connect  the  cerebrum  with  the 
medulla  oblongata,  pons  Varolii,  and  spinal  cord.  These 
are  the  crura  cerebri  or  cerebral  peduncles ;  hence  the 
group  is  described  as  the  peduncular  fibres.  It  will  be 
remembered  that  the  crura  cerebri  consist  of  the  crusta 
and  tegmentum.  The  fibres  which  come  from  the  pyra- 
mids of  the  medulla  and  are  continued  through  the  pons 
aid  in  forming  the  crusta.  To  these  fibres  are  added 
others  which  originate  in  the  gray  matter  of  the  aqueduct 
of  Sylvius  and  in  the  locus  niger. 

After  forming  the  crura  cerebri  the  fibres  pass  upward  : 
some  of  them  go  directly  to  the  gray  matter  of  the  cor- 
tex :  these  form  the  corona  radiata ;  others  go  to  the 
internal  capsule,  and  thence  to  the  corpora  striata,  where 
they  terminate ;  while  some  of  the  others  continue  on, 
receiving  fibres  from  these  bodies,  and  together  they 
assist  in  forming  the  corona  radiata.  More  fibres  come 
from  the  corpora  striata  than  end  there,  so  that  the 
number  of  those  which  emerge  is  greater  than  the 
number  of  those  which  enter. 

The  tegmentum  of  the  crus  is  made  up  of  fibres  from 
the  anterior  and  lateral  columns  of  the  cord,  the  olivary 


268  HUMAN  PHYSIOLOGY. 

body,  funiculus  cuneatus,  funiculus  gracilis,  corpora 
quadrigemina,  corpora  geniculata,  and  superior  pedun- 
cles of  the  cerebellum.  These  fibres  pass  into  the  optic 
thalami,  some  terminating  there,  while  others  pass 
through.  To  these  latter  are  added  fibres  having  their 
origin  in  the  optic  thalami,  and  together  they  assist  in 
forming  the  corona  radiata,  being  traced  to  the  cells  in 
the  cortical  substance  of  the  temporo-sphenoidal  and 
occipital  lobes. 

2.  The  second  group  of  fibres  in  the  cerebrum  consists 
of  those  which  connect  the  hemispheres  and  the  basal 
ganglia,  and  are  the  transverse  commissural  fibres. 
They  compose  the  corpus  callosum  and  anterior  and 
posterior  commissures.  The  fibres  of  the  corpus  cal- 
losum connect  the  hemispheres,  being  traced  into  the 
convolutions  and  intersecting  those  of  the  corona  ra- 
diata. The  anterior  commissure  connects  the  corpora 
striata,  and  then  passes  through  these  bodies  into  the 
temporo-sphenoidal  lobe.  Some  of  the  fibres  of  the 
posterior  commissure  connect  the  optic  thalami,  while 
some  come  from  the  tegmentum  of  one  side,  traverse 
the  optic  thalamus,  and  terminate  in  the  white  matter 
of  the  temporo-sphenoidal  lobe  of  the  other  side. 

3.  The  third  group  consists  of  fibres  called  "  arcu- 
ate "  or  association  fibres,  and  those  called  "  longitudi- 
nal "  or  "  collateral "  fibres.  The  arcuate  fibres,  which 
connect  adjacent  convolutions,  are  situated  just  beneath 
the  cortical  substance.  As  representatives  of  the  longi- 
tudinal group  there  may  be  mentioned  the  taenia  semi- 
circularis  and  the  fornix. 

Functions  of  the  Cerebrum. — That  the  cerebrum  is 
not  essential  to  life  has  been  demonstrated  experiment- 
ally many  times  in  birds,  fishes,  rabbits,  rats,  and  other 


NERVOUS  FUNCTIONS.  269 

animals.  Of  course  the  same  kind  of  proof  is  not 
available  in  man,  but  there  are  instances  on  record  in 
which  the  destruction  of  brain-tissue  has  been  so  great 
as  to  warrant  the  statement  that  in  man,  as  well  as  in 
lower  animals,  life  may  be  maintained  without  the  influ- 
ence of  the  cerebrum.  Perhaps  the  most  remarkable  in- 
stance is  that  of  a  man  whose  skull  is  now  in  the  War- 
ren Anatomical  Museum.  This  man  was  injured  by  a 
premature  blast,  the  iron  bar,  one  inch  in  diameter,  which 
was  used  in  tamping  being  driven  through  the  skull  and 
brain.  Although  delirious  and  unconscious  for  several 
weeks,  he  finally  recovered,  with  but  the  loss  of  one  eye. 
He  lived  more  than  twenty  years  after  the  injury  and 
performed  the  work  of  a  coachman  and  farm-laborer. 

The  cerebrum  is  undoubtedly  the  seat  of  the  intel- 
lectual faculties.  A  study  of  the  lower  animals  reveals 
the  fact  that  according  as  the  hemispheres  are  developed 
the  signs  of  intelligence  are  increased :  when  these 
structures  are  destroyed  there  is  an  absence  of  these 
manifestations. 

When  the  hemispheres  are  removed  there  is  no  spon- 
taneous action.  In  studying  the  reflex  action  of  the 
spinal  cord  in  a  decapitated  frog  it  was  seen  that  the 
animal  made  no  attempt  to  move  or  change  its  position 
unless  some  stimulus  was  applied,  and  that  as  soon  as 
this  stimulus  was  withdrawn  it  lapsed  into  its  original 
position,  remaining  therein  until  again  disturbed.  If 
the  hemispheres  be  removed  from  a  pigeon,  it  will  act 
very  much  as  does  the  frog.  If  disturbed  it  may  fly 
for  a  short  distance,  but  at  once  lapses  into  a  state  of 
apparent  unconsciousness,  with  eyes  closed.  When  the 
foot  is  pinched  it  will  be  withdrawn.  If  a  pistol  be  dis- 
charged, the  bird  will  open  its  eyes  and  show  unmis- 


270  HUMAN  PHYSIOLOGY. 

takably  that  the  report  was  heard,  but  the  discharge 
seems  to  produce  no  other  effect.  The  fact  that  there  is 
danger  is  not  appreciated.  It  seems,  therefore,  that  the 
faculty  is  absent  by  which  the  bird  in  health  associates 
danger  with  such  sounds.  When  the  human  brain  is 
diseased  or  injured,  something  of  the  same  kind  is  wit- 
nessed, and  in  idiots,  whose  brains  are  imperfectly 
developed,  the  intellectual  faculties  are  very  deficient. 
Human  intelligence  is  manifested  through  memory, 
reason,  and  judgment. 

Memory  is  the  basis  for  the  action  of  the  other  two  fac- 
ulties; without  it  there  could  be  neither  reason  nor  judg- 
ment. It  is  the  faculty  of  the  mind  by  which  it  retains 
the  knowledge  of  previous  thoughts  or  events,  the  actual 
and  distinct  retention  and  recognition  of  past  ideas  in 
the  mind.  Afferent  impulses  are  continually  reaching 
the  cells  of  the  cortex  of  the  brain,  and  these  impulses 
produce  impressions  more  or  less  permanent.  ]f  they 
were  evanescent,  passing  away  almost  as  soon  as  re- 
ceived, memory  would  be  impossible,  but  it  is  this 
retention  which  constitutes  memory.  If  the  ideas  pro- 
duced by  these  impulses  come  again  into  existence  spon- 
taneously and  without  effort,  this  is  remembrance ;  if  it 
require  an  effort,  this  is  recollection,  a  re-collecting  of 
the  impressions  originally  produced  on  the  cells  by  the 
afferent  impulses. 

Reason  is  that  faculty  of  the  mind  by  which  is  ap- 
preciated the  nature  of  nervous  impulses,  and  by  which 
they  are  referred  to  their  external  source — by  which  an 
effect  is  referred  to  its  cause.  This  reference  an  idiot 
cannot  make ;  hence  he  is  said  to  be  "  un-reasonable." 

Judgment  is  the  faculty  of  the  mind  by  which  a  selec- 
tion is  made  of  the  proper  means  to  be   used  in  the 


NERVOUS  FUNCTIONS.  2/1 

attainment  of  a  particular  end.  Thus  if  one  select  inad- 
equate means  for  the  accomplishment  of  a  given  object, 
it  is  said  that  one  "  lacks  judgment." 

The  cerebrum  is  the  seat  of  conscious  sensation,  as 
opposed  to  sensation  alone.  The  gray  matter  of  the 
spinal  cord  is  said  to  be  sensitive;  that  is,  it  responds 
to  stimuli.  If  the  finger  be  burned,  the  afferent  impulse 
is  received  by  the  gray  matter  of  the  cord  and  a  motor 
impulse  passes  out  to  the  muscles.  But  if  the  impulse 
travel  no  farther  than  the  cord,  there  is  no  conscious 
sensation.  To  excite  this  sensation  it  must  proceed  to 
the  gray  matter  of  the  cerebral  cortex.  It  is  in  the  cells 
of  the  cortex  also  that  volitional  impulses  have  their  origin. 
The  gray  matter,  then,  is  the  seat  of  the  will  as  well 
as  the  conscious  centre,  and  when  largely  diseased  or 
destroyed  the  only  movements  made  are  involuntary, 
depending  on  other  nerve-centres. 

Cerebral  Localization. — Although  the  study  of  the 
intellectual  faculties  is  both  difficult  and  abstruse,  much 
advance  has  in  late  years  been  made  in  the  knowledge 
of  the  physiology  of  the  cerebrum,  so  far  as  it  relates  to 
the  production  of  voluntary  movements.  Observations 
upon  both  man  and  the  lower  animals  lead  one  to  be- 
lieve that  the  power  of  producing  certain  movements  is 
limited  to  certain  restricted  areas  of  the  brain.  This 
power  is  known  as  cerebral  localization. 

These  observations  had  their  beginning  in  1870.  It 
was  found  that  when  galvanic  currents  were  applied  to 
certain  parts  of  the  cerebral  convolutions  movements  of 
particular  muscles  followed,  and  that  in  order  to  excite 
these  muscles  these  parts  or  areas  must  be  stimulated. 
Although  the  dog  was  first  experimented  upon,  other 
animals  (cat,  rabbit,  and  monkey)  have  furnished  like  re- 


272 


HUMAN  PHYSIOLOGY. 


suits.  In  the  application  of  these  experiments  the  animal 
is  put  under  ether,  the  skull  is  trephined,  and  the  poles  of 
a  galvanic  battery  are  applied  to  the  convolutions.  When 
on  such  application  to  a  given  spot  or  area  contractions  of 
certain  muscles  or  groups  of  muscles  follow,  such  spot  or 
area  is  said  to  be  the  centre  of  motion  for  these  muscles. 

The  following  statement  may  be  said  to  summarize 
what  is  established  with  reference  to  cerebral  localization : 

In  general  the  motor  area  is  the  region  of  the  convo- 
lutions in  the  neighborhood  of  the  fissure  of  Rolando. 


Fig.  56. — The  Motor  Areas  on  the  Outer  Surface  of  the  Braiu. 


In  this  area  are  centres  of  motion  for  the  movements 
of  the  arms  and  legs  (Figs.  56,  57),  as  in  swimming,  for 
extension  forward  of  the  arm  and  hand,  for  supination 
of  the  hand,  and  for  flexion  of  the  forearm.  Around 
the  lower  part  of  this  fissure  are  the  centres  for  the 
movements  of  the  mouth  and  tongue.  The  destruction 
of  these  convolutions  or  the  presence  in  them  of  lesions 
results  in  paralysis  of  motion  in  these  parts.     Of  course 


NERVOUS  FUNCTIONS:  273 

the  action  is  in  all  cases  crossed ;  that  is,  excitation  of 
one  side  of  the  cerebrum  causes  the  movements  spoken 


Fig.  57. — The  Motor  Areas  on  the  Median  Surface  of  the  Brain. 

of  on  the  opposite  side  of  the  body,  and  the  same  is  true 
of  the  paralysis  which  follows  disease  or  injury. 

Centre  for  Speech. — Articulate  speech  requires  the  ex- 
ercise of  memory  and  the  power  of  producing  certain  vol- 
untary movements.  Inability  to  produce  articulate  speech 
is  known  as  aphasia.  If  the  memory  of  words  be  absent 
while  the  power  to  produce  the  movements  remains,  it 
is  called  "  amnesic  aphasia,"  and  if  the  reverse  condition 
exist,  it  is  termed  "  ataxic  aphasia."  It  is  believed  that 
the  centre  which  presides  over  language  is  in  the  frontal 
lobe  on  the  left  side.  Some  localize  it  in  the  third  fron- 
tal convolution ;  others  regard  it  as  being  more  diffused, 
and  locate  the  centre  in  the  convolutions  surrounding 
the  lower  end  of  the  fissure  of  Sylvius. 

Sensory  Areas. — While  the  motor  areas  appear  to  be 
localized,  the  same  is  not  true  for  those  areas  that  are 

18 


274  HUMAN  PHYSIOLOGY. 

sensory.  If  the  superior  temporo-sphenoidal  convolu- 
tion be  stimulated  in  its  posterior  part,  the  animal  pricks 
up  its  ear  and  turns  its  head  to  the  opposite  side,  sug- 
gestive of  the  idea  that  it  has  heard  with  that  ear.  If 
these  convolutions  on  both  sides  be  destroyed,  perma- 
nent deafness  results,  while  if  only  one  convolution  be 
destroyed,  there  is  loss  of  hearing  on  the  opposite  side : 
this  part  of  the  brain  has  been  described  as  the  auditory 
centre.  A  movement  of  the  head  and  eyes,  suggesting 
that  the  sense  of  sight  has  been  excited,  occurs  when 
the  occipital  lobes  and  angular  convolutions  are  stimu- 
lated. If  one  occipital  lobe  be  destroyed,  hemiopia  re- 
sults :  this  is  regarded  as  the  visual  or  optic  centre.  The 
olfactory  cetitre  is  located  in  the  anterior  extremity  of 
the  uncinate  gyrus.  The  taste  or  gustatory  centre  has 
not  been  localized. 

Functions  of  Corpora  Quadrigemina. — The  corpora 
quadrigemina  are  the  centres  for  visual  sensations.  If 
they  be  destroyed,  the  sense  of  sight  is  lost ;  if  they 
become  seriously  diseased,  blindness  results.  They  are 
regarded  also  as  the  centres  which  govern  the  move- 
ments of  the  iris  :  when  they  are  stimulated  the  pupil 
contracts,  while  it  dilates  if  they  are  removed.  In  them 
is  also  the  centre  for  the  co-ordination  of  the  movements 
of  the  eyes. 

Functions  of  Corpora  Striata  and  Optic  Thalami. — The 
corpora  striata  have  been  spoken  of  as  the  great  motor 
ganglia  at  the  base  of  the  brain,  probably  because  lesions 
of  them  produce  hemiplegia,  but  this  is  due  to  pressure 
on  the  internal  capsule.  The  optic  thalami  have  also 
been  regarded  as  great  sensory  centres,  but  if  lesions  of 
them  produce  loss  of  sensation,  it  is  due  to  an  interfe- 
rence with  the  posterior  limb  of  the  internal  capsule.    In 


NERVOUS  FUNCTIONS. 


275 


general  it  may  be  said  that  the  functions  of  these  basal 
ganglia  are  not  understood. 

Cranial  Nerves. — The  cranial  nerves  have  their  origin 
in  the  gray  matter  at  the  base  of  the  brain,  and  they 


Fig.  58. — Base  of  Brain:  i,  2,  3,  cerebrum;  4  and  5,  longitudinal  fissure;  6,  fissure 
of  Sylvius  ;  7,  anterior  perforated  spaces  ;  8,  infundibulum  ;  9,  corpora  albicantia ; 
10,  posterior  perforated  space;  11,  crura  cerebri;  12,  pons  Varolii ;  13,  junction  of 
spinal  cord  and  medulla  oblongata  ;  14,  anterior  pyramid  ;  14*,  decussation  of  ante- 
riorpyramid;  15,  olivary  body  ;  16,  resti  form  body  ;  17,  cerebellum;  ig,  crura  cerebelli ; 
21,  olfactory  sulcus  ;  22,  olfactory  tract ;  23,  olfactory  bulbs  ;  24,  optic  commissure  ;  25, 
motor  oculi  nerve  ;  26,  patheticus  nerve  ;  27,  trigeminus  nerve  ;  28,  abducens  nerve  ; 
29,  facial  nerve  ;  30,  auditory  nerve  ;  31,  glosso-pharyngeal  nerve  ;  32,  pneumogastric 
nerve  ;  33,  spinal  accessory  nerve  ;   34,  hypoglossal  nerve. 

escape  from  the  skull  by  various  openings,  called  "  foram- 
ina," to  reach  the  parts  to  which  they  are  distributed. 


276  HUMAN  PHYSIOLOGY. 

The  only  exception  to  this  is  the  spinal  accessory,  a  part 
of  which  arises  from  the  gray  matter  of  the  cord. 
Among  the  cranial  nerves  are  those  of  special  sense, 
of  motion,  and  nerves  having  both  motor  and  sensory 
properties  (Fig.  58).  The  points  at  which  they  leave 
the  brain  are  spoken  of  as  their  "  apparent  origin,"  but 
this  is  only  apparent,  for  they  can  be  traced  into  the 
brain-substance,  to  collections  of  nerve-cells,  nerve-cen- 
tres, to  which  the  name  "  nuclei  "  has  been  given.  The 
nucleus  of  a  nerve  is  its  real  origin. 

Of  cranial  nerves  there  are  twelve  pairs,  the  number  in- 
dicating the  order  from  before  backward  in  which  they 
escape  from  the  cavity  of  the  cranium:  i.  Olfactory; 
2,  Optic;  3,  Motor  oculi  communis;  4,  Patheticus ;  5, 
Trigeminus ;  6,  Abducens ;  7,  Facial ;  8,  Auditory ;  9, 
Glosso -pharyngeal ;  10,  PneumiOgastric ;  ii,  Spinal  ac- 
cessory;  12,  Hypoglossal. 

1.  Olfactory  Nerve. — The  olfactory  nerve  is  a  term 
formerly  applied  to  what  is  more  properly  the  olfac- 
tory tract.  This  tract  is  a  part  of  the  brain  lying  in  a 
groove,  the  olfactory  sulcus,  on  the  under  surface  of  the 
frontal  lobe,  and  it  may  be  considered  as  a  process  from 
that  lobe.  In  some  animals  it  is  of  such  size  that  it  is 
called  the  "  olfactory  lobe."  In  man  it  is  hardly  large 
enough  to  merit  this  title.  It  is  composed  principally 
of  gray  matter,  with  some  white.  At  the  central  or 
posterior  extremity  the  tract  is  connected  with  the  rest 
of  the  brain  by  three  roots,  the  real  origin  of  which  is  as 
yet  undetermined.  At  the  anterior  extremity  the  tract 
expands  to  form  the  olfactory  bulb,  which  lies  upon  the 
cribriform  plate  of  the  ethmoid  bone,  and  which  contains 
nerve-cells.  From  the  under  surface  of  the  bulb  are  given 
off  the  true  olfactory  nerves,  from  fifteen  to  twenty  in  num- 


NERVOUS  FUNCTIONS.  2/7 

ber.  These  nerves  are  composed  of  non-medullated  fibres, 
axis-cylinders  with  a  sheath,  but  with  no  white  substance 
of  Schwann.  They  pass  out  from  the  cavity  of  the  cra- 
nium through  the  cribriform  foramina,  and  are  distrib- 
uted to  the  olfactory  membrane ;  that  is,  that  portion  of 
the  mucous  membrane  of  the  nose  (Schneiderian  mem- 
brane) which  covers  the  superior  and  middle  turbinated 
bones  and  the  upper  part  of  the  septum  nasi.  The 
Schneiderian  membrane  lines  the  nasal  fossae.  Before 
the  time  of  Schneider,  from  whom  the  membrane  was 
named,  it  was  thought  that  the  secretion  it  forms  came 
from  the  brain  :  he  demonstrated  that  it  came  from  the 
membrane  itself  It  is  covered  by  epithelium,  which, 
near  the  orifice  of  the  nostril  in  the  vestibule,  is  pave- 
ment, but  elsewhere,  except  on  the  olfactory  membrane, 
this  epithelium  is  columnar  and  ciliated.  On  the  olfac- 
tory membrane  the  cells  are  columnar,  but  in  general 
not  ciliated.  Between  these  cells  are  the  olfactory  cells 
of  Schultze,  with  which  the  olfactory  nerves,  after  form- 
ing a  plexus,  are  believed  to  be  in  communication. 

Function  of  the  Olfactory  Newe. — The  function  of  the 
olfactory  nerve  is  to  preside  over  the  sense  of  smell, 
which  will  be  discussed  in  the  consideration  of  the 
senses. 

2.  Optic  Nerve. — The  optic  nerve  is  distributed  to  the 
eyeball.  Followed  backward,  the  nerves  from  both  eyes 
are  seen  to  unite  to  form  the  optic  commissure,  from 
which  goes  off  on  each  side  an  optic  tract.  The  optic 
tract  just  before  its  connection  with  the  brain  divides 
into  two  parts.  One  of  these  divisions  or  bands  has  its 
origin  in  the  corpora  quadrigemina,  and  the  other  in  the 
optic  thalamus,  the  latter  receiving  fibres  from  the  inner 
corpus  geniculatum. 


2/8  HUMAN  PHYSIOLOGY. 

The  structure  of  the  commissure,  or  chiasma,  is  quite 
complex.  It  consists  of  nerve-fibres  which  pass  (i)  from 
one  retina  to  the  other,  inter-retinal  fibres ;  (2)  from  one 
side  of  the  brain  to  the  other,  intercerebral  fibres ;  (3) 
from  the  brain  to  the  retina  of  the  same  side ;  (4)  from 
one  side  of  the  brain  to  the  retina  of  the  other  side. 

Fimctiojt  of  the  Optic  Nerve. — The  optic  nerve  is  the 
special  nerve  of  the  sense  of  sight.  Its  sole  function  is 
to  convey  to  the  brain  the  impulses  received  from  the 
retina,  produced  there  by  the  luminous  rays  falling  upon 
them.  These  impulses  when  they  reach  the  brain  cause 
the  sensation  of  light.  If  the  optic  nerves  be  divided, 
blindness  results.  The  optic  nerve  is  also  intimately 
connected  with  the  movements  of  the  iris,  which  move- 
ments result  in  changes  of  the  size  of  the  pupil.  This 
is  a  reflex  act  in  which  the  optic  serves  as  the  afferent 
nerve.  The  modus  operandi  will  be  better  understood 
after  a  description  of  the  motor  oculi.  (For  a  further 
discussion  of  this  nerve  and  its  function  the  reader  is 
referred  to  the  discussion  of  the  sense  of  Sight.) 

3.  Motor  Oculi. — The  third  nerve  (motor  oculi,  motor 
oculi  communis,  or  oculo-motorius)  leaves  the  surface 
of  the  brain  at  the  inner  surface  of  the  crus  cerebri,  just 
in  front  of  the  pons  Varolii.  Its  real  origin  is,  however, 
a  nucleus  in  the  floor  of  the  aqueduct  of  Sylvius.  It  es- 
capes from  the  cranium  through  the  sphenoidal  fissure, 
and  is  distributed  to  the  superior,  internal,  and  inferior 
recti  and  to  the  inferior  oblique.  It  also  supplies  the 
levator  palpebrse  superioris,  and  sends  a  branch  to  the 
ophthalmic,  lenticular,  or  ciliary  ganglion.  Another 
way  to  describe  its  distribution  is  to  say  that  it  supplies 
the  levator  palpebrae  and  all  the  muscles  that  move  the 
eyeball,  except  the  superior  oblique  and  external  rectus. 


NERVOUS  FUNCTIONS.  279 

The  action  of  these  muscles  is  largely  indicated  by 
their  names.  The  levator  palpebrae  by  its  contraction 
raises  the  upper  eyelid.  The  internal  rectus  turns  the 
eyeball  inward  toward  the  nose,  and  the  external  rectus 
turns  it  outward.  The  direction  and  the  point  of  attach- 
ment of  the  superior  rectus  are  such  that  when  it  con- 
tracts the  eyeball  is  not  only  turned  upward,  but  it  is 
also  slightly  rotated  inward ;  this  is  corrected  by  the 
action  of  the  inferior  oblique,  so  that  the  two  acting 
together  produce  a  movement  directly  upward.  The 
same  deviation  inward  follows  when  the  eye  is  turned 
downward  by  the  inferior  rectus,  and  a  similar  correction 
is  made  by  the  action  of  the  superior  oblique.  If  the 
external  and  superior  recti  act  together,  the  movement 
of  the  eyeball  is  in  the  direction  of  the  diagonal — that  is, 
outward  and  upward;  the  conjoint  action  of  the  external 
and  inferior  recti  causes  the  eyeball  to  move  outward 
and  downward,  and  a  corresponding  action  results  when 
the  other  adjacent  recti  are  brought  into  play.  If  the 
recti  act  alternately,  the  eyeball  will  be  rotated  com- 
pletely, as  in  looking  around  a  room  from  one  side  to 
the  other  and  back  again,  from  the  floor  to  the  ceiling. 
The  motor  oculi  is  purely  a  motor  nerve.  When  stim- 
ulated, contraction  is  produced  in  the  muscles  to  which 
it  is  distributed ;  when  the  nerve  is  divided,  these  muscles 
are  paralyzed. 

Paralysis  of  the  Motor  Oculi. — When  the  motor  oculi 
is  paralyzed  the  following  are  the  results : 

{a)  External  strabismus,  which  consists  in  a  turning 
of  the  eye  outward.  The  retention  of  the  eye  in  its 
normal  position  requires  the  conjoint  action  of  the 
internal  and  external  recti.  In  paralysis  of  the  motor 
oculi  the  internal   rectus   has  lost  its   innervation,  and 


280  HUMAN  PHYSIOLOGY. 

therefore  its  power  to  contract,  and  the  external  rectus, 
which  receives  its  nervous  supply  from  another  nerve  (the 
abducens),  having  lost  its  antagonist,  turns  the  eye  outward. 

{b)  Liiscitas. — After  external  strabismus  has  been  pro- 
duced the  eye  remains  in  that  condition,  for  the  muscles 
which  could  move  it  in  any  other  direction  have  been 
paralyzed.     This  immobility  is  called  "  luscitas." 

{c)  Ptosis. — The  levator  palpebrae  superioris  is  also 
paralyzed,  and  the  upper  eyelid  droops,  constituting 
ptosis.  The  ability  to  close  the  eye  still  remains,  as 
this  is  the  act  of  the  orbicularis  palpebrarum,  which  is 
not  innervated  by  the  third  but  by  the  seventh  nerve. 

id)  Mydriasis. — A  branch  of  the  motor  oculi  goes  to 
the  ciliary  ganglion,  which  gives  off  the  ciliary  nerves 
that  supply  the  iris.  Accompanying  the  manifestations 
of  paralysis  of  the  motor  oculi  already  mentioned  there 
is  in  addition  a  dilatation  of  the  pupil,  or  mydriasis. 
The  diminution  of  the  size  of  the  pupil  following  the 
action  of  light  upon  the  retina  does  not  take  place  when 
this  nerve  is  paralyzed.  The  contraction  of  the  pupil 
is  a  reflex  act  requiring  the  integrity  of  the  optic  nerve, 
which  serves  as  a  carrier  of  the  luminous  impressions 
to  the  brain,  and  the  motor  oculi,  which  is  the  efferent 
nerve  in  this  act. 

{e)  Inability  to  Focus. — The  muscle  concerned  in  focus- 
ing the  eye  for  short  distances  is  the  ciliary.  The  power 
to  focus  is  lost  in  paralysis  of  the  motor  oculi.  This 
paralysis  in  human  beings  may  be  due  to  disease  of  the 
brain  or  to  pressure  on  the  nerves.  If  the  trunk  of  the 
nerve  be  affected,  all  the  physical  signs  mentioned  may 
be  observed,  while  if  a  single  branch  only  be  involved,  the 
effect  will  be  seen  only  in  the  part  to  which  that  branch 
is  distributed. 


NERVOUS  FUNCTIONS.  28 1 

4,  Trochlearis. — The  apparent  origin  of  the  trochlearis 
or  patheticus  is  on  the  outer  side  of  the  crus  cerebri,  in 
front  of  the  pons,  and  its  real  origin  is  a  nucleus  con- 
tinuous with  that  of  the  motor  oculi.  The  trochlearis 
leaves  the  cranium  by  the  sphenoidal  fissure,  and  is  dis- 
tributed to  but  one  muscle,  the  superior  oblique.  When 
this  nerve  is  paralyzed,  the  patient  cannot  turn  the  eye 
outward  and  downward,  the  action  of  the  superior  ob- 
lique is,  therefore,  to  turn  the  eye  outward  and  downward. 
If  the  head  be  not  turned  toward  either  side  when  this 
nerve  is  paralyzed,  the  only  thing  observable  is  that  the 
patient  sees  double  when  he  looks  downward,  and  the 
image  perceived  by  the  affected  eye  is  oblique  and  below 
that  seen  by  the  eye  that  is  unaffected. 

5.  Trigeminus. — This  nerve,  which  is  also  called  "tri- 
facial," has  received  its  names  from  the  fact  that  it  has 
three  subdivisions,  and  is  distributed  in  the  main  to  the 
parts  about  the  face.  It  arises  by  two  roots,  anterior 
and  posterior.  The  anterior  root,  the  smaller,  is  purely 
motor ;  the  posterior  root,  the  larger,  is  sensory,  and 
is  characterized  anatomically  by  having  upon  it  the 
Gasserian  ganglion.  The  nerve  leaves  the  brain  at  the 
side  of  the  pons  Varolii.  The  real  origin  of  the  motor 
root  is  a  nucleus  in  the  floor  of  the  fourth  ventricle ; 
the  sensory  root  arises  from  a  nucleus  on  a  level  with 
the  middle  of  the  superior  peduncle  of  the  cerebellum, 
just  internal  to  the  margin  of  the  fourth  ventricle. 
Some  authorities  give  it  a  more  extensive  origin, 
from  the  pons  through  the  medulla  and  as  far  as  the 
posterior  cornua  of  the  gray  matter  of  the  spinal  cord. 

The  motor  root  passes  beneath  the  Gasserian  ganglion, 
and  takes  no  part  in  the  formation. 

Beyond  the  ganglion  the  fifth  nerve  divides  into  three 


282  HUMAN  PHYSIOLOGY. 

parts:  (i)  ophthalmic;   (2)  superior  maxillary;  and  (3) 
inferior  maxillary. 

(l)   Ophthalmic  Divisioii. — This  division,  which  leaves 
the  cranium  by  the  sphenoidal  fissure,  is  distributed  to 


Fig.  59. — General  Plan  of  the  Branches  of  the  Fifth  Pair:  i,  lesser  root  of  the  fifth 
P^ir  ;  2)  greater  root,  passing  forward  into  the  Gasserian  ganglion  ;  3,  placed  on  the 
bone  above  the  ophthalmic  divison,  which  is  seen  dividing  into  the  supraorbital,  lach- 
rymal, and  nasal  branches,  the  latter  connected  with  the  ophthalmic  ganglion  ; 
4,  placed  on  the  bone  close  to  the  foramen  rotundum,  marks  the  superior  maxillary 
division;  5,  placed  on  the  bone  over  the  foramen  ovale,  marks  the  inferior  max- 
illary division  (after  a  sketch  by  Charles  Bell). 

the  tentorium  cerebelli,  the  eyeball,  the  Schneiderian 
membrane,  the  lachrymal  gland,  and  the  skin  about  the 
forehead  and  nose.  It  also  supplies  branches  to  the 
ciliary  ganglion,  and  contains  only  fibres  from  the  pos- 
terior root,  none  from  the  anterior. 

(2)  Superior  Maxillary  Division. — This  division  of  the 
fifth  pair  leaves  the  cranial  cavity  by  the  foramen  rotun- 


NERVOUS  FUNCTIONS.  283 

dum.  It  is  distributed  to  the  dura  mater,  the  spheno- 
palatine ganglion  (Meckel's),  the  skin  of  the  temple  and 
cheek,  the  teeth,  the  gums,  and  the  mucous  membrane 
of  the  upper  jaw  and  upper  lip,  the  mucous  membrane 
of  the  lower  part  of  the  nasal  passages,  the  skin  of  the 
lower  eyelid,  side  of  nose,  and  upper  lip.  There  are  no 
fibres  of  the  anterior  root  in  this  division. 

(3)  Inferior  Maxillary  Division. — As  has  already  been 
stated,  there  is  no  anatomical  connection  between  the 
motor  root  of  the  fifth  nerve  and  the  Gasserian  ganglion. 
From  this  ganglion  are  given  off  nerve-fibres  which  join 
the  motor  root,  together  making  the  inferior  maxil- 
lary division,  which  escapes  through  the  foramen  ovale. 
It  is  distributed  to  the  dura  mater,  the  otic  ganglion, 
the  mucous  membrane  of  the  cheek,  skin,  and  mucous 
membrane  of  the  lower  lip,  the  anterior  wall  of  the 
external  auditory  meatus,  the  front  of  the  external  ear 
and  the  skin  of  the  adjacent  temporal  region,  the  sub- 
maxillary gland  and  ganglion,  the  mucous  membrane 
of  the  mouth  and  tongue ;  and  to  the  papillae  at  the  tip, 
the  edges,  and  anterior  two-thirds  of  the  tongue,  the 
teeth  and  gums  of  the  lower  jaw.  It  also  supplies  the 
following  muscles :  temporal,  masseter,  pterygoid, 
mylo-hyoid,  and  anterior  belly  of  the  digastric. 

Physiological  Properties  of  the  Trigeminus. — The  tri- 
geminus is  the  largest  of  the  cranial  nerves,  and  its 
functions  are  many  and  important.  It  supplies  the 
parts  to  which  it  is  distributed  with  the  general  sen- 
sibility they  possess.  If  it  be  divided,  there  is  com- 
plete absence  of  sensation  (anaesthesia)  of  the  face  on 
the  corresponding  side  (Fig.  59).  So  pronounced  is 
this  anaesthesia  that  no  amount  of  irritation  applied  to 
such  ordinarily  sensitive  parts  as  the  cornea  will  pro- 


284 


HUMAN  PHYSIOLOGY. 


duce  any  effect.  An  animal  thus  experimented  upon 
seems  entirely  oblivious  of  the  irritation.  Experiment- 
ers have  gone  so  far  as  to  exsect  the  eyeball  and  apply 


Figs.  6o,  6i. — Distribution  of  the  Cutaneous  Sensitive  Nerves  upon  the  Head:  oma, 
omi,  the  occipit.  maj.  and  minor  (from  the  N.  cervical  II.  and  III.);  a7n,  N.  auric- 
ular magn.  (from  N.  cervic.  III.);  cs,  N.  cervical  superfic.  (from  N.  cervic.  III.); 
Ki,  first  branch  of  the  fifth  {so,  N.  supraorbit. ;  st,  N.  supratrochl. ;  it,  N.  infra- 
trochl.  ;  e,  N.  ethmoid. ;  /,  N.  lachrymal.);  V^,  second  branch  of  the  fifth  [sm,  N. 
subcutan.  malse  seu  zygomaticus) ;  V^,  third  branch  of  fifth  {at,  N.  auriculo-tempor.; 
b,  N.  buccinator;  wz,  N.  mental.);  B,  posterior  branches  of  the  cervical  nerves. 


hot  irons  to  the  skin  without  causing  pain  to  the  animal 
experimented  upon. 

Neuralgia  of  the  face,  headache,  and  toothache  are  all 
due  to  some  interference  with  the  normal  functions  of 
this  nerve.  It  is  not  an  uncommon  thing  to  hear  patients 
complain  of  headaches  which  seem  to  them  to  be  in  the 
brain  itself  These  deep-seated  headaches  may  be  due 
to  affections  of  one  or  more  of  the  recurrent  branches 
which  come  off  from  the  divisions  of  the  nerve,  and 


NERVOUS  FUNCTIONS.  285 

which  are  distributed  to  the  dura  mater  and  bones  of 
the  skull. 

Lingual  {Gustatory)  Nerve. — This  nerve  is  sometimes 
called  the  "  lingual  branch  of  the  fifth  nerve."  It  is  the 
branch  which  is  distributed  to  the  mucous  membrane 
of  the  mouth  and  the  gums,  and  to  the  mucous  mem- 
brane and  papillae  of  the  tongue.  It  supplies  the  tongue 
with  tactile  sensibility,  a  quality  of  great  advantage  in 
enabling  one  to  detect  the  physical  properties  of  food,  to 
recognize  in  it  the  presence  of  hard  objects  which  it 
would  be  injurious  to  swallow,  and  to  determine  when 
it  is  ready  for  deglutition.  Besides  this  tactile  sensibility 
the  lingual  nerve  supplies  the  anterior  two-thirds  of  the 
tongue  with  the  sense  of  taste,  a  special  sense,  and  this 
power  is  lost  when  the  fifth  pair  or  the  lingual  branch  is 
divided. 

Mastication. — The  muscles  that  have  been  mentioned 
as  receiving  branches  of  the  inferior  maxillary  division 
are  those  concerned  in  the  act  of  mastication.  In  this 
act  the  temporal  and  masseter  close  the  mouth,  the  mylo- 
hyoid and  digastric  open  it,  while  the  pterygoids  produce 
the  lateral  movement  of  the  lower  jaw.  Division  of  the 
inferior  maxillary  paralyzes,  therefore,  all  these  muscles. 
If  it  be  divided  on  one  side,  the  muscles  on  the  other 
side  can  still  perform  the  act,  but  in  an  imperfect  man- 
ner; if  divided  on  both  sides,  all  masticatory  movements 
will  be  abolished. 

Anastomosis  of  tJie  Fifth  Pair. — Besides  the  branches 
already  mentioned,  there  are  others  which  are  termed 
anastomotic  branches.  Although  the  upper,  middle,  and 
lower  parts  of  the  face  are  supplied  with  sensation  by 
the  ophthalmic,  superior  maxillary,  and  inferior  maxil- 
lary divisions  respectively,  still  the  boundaries  of  each 


286  HUMAN  PHYSIOLOGY. 

are  not  absolute.  Thus  the  skin  of  the  nose  is  supplied 
by  fibres  fi-om  the  ophthalmic  and  superior  maxillary, 
and  the  skin  of  the  temporal  region  is  supplied  from  both 
the  superior  and  inferior  maxillary  divisions.  In  addition 
to  these  branches,  there  are  some  which  unite  with  other 
nerves  and  give  a  certain  amount  of  sensibility  to  the 
parts  to  which  these  nerves  are  distributed.  A  striking 
instance  of  this  is  the  branch  which  anastomoses  with 
the  facial  nerve.  This  nerve  is  at  its  origin  purely  motor, 
and  is  distributed  to  the  muscles  of  the  face.  These 
muscles  are  endowed  with  sensibility,  but  this  is  not  due 
to  fibres  of  the  facial  nerve,  but  to  those  of  the  fifth 
nerve,  which  anastomose  with  the  facial  and  go  with  it 
to  its  termination  in  the  muscles. 

Connection  of  the  Fifth  Pair  ivith  the  Special  Senses. — 
After  division  of  the  fifth  nerve  the  special  senses  of 
smell,  sight,  taste,  and  hearing  are  seriously  affected. 
The  Schneiderian  membrane  becomes  swollen,  and  later 
assumes  a  fungous  condition  and  bleeds  readily  when 
touched.  There  is  also  an  accumulation  of-  altered 
mucus  in  the  nasal  passages.  The  eye  also  undergoes 
marked  changes:  the  conjunctiva  becomes  congested 
and  the  cornea  opaque ;  later,  mo.st  of  the  structures  of 
the  eye  suffer  from  inflammatory  changes  to  the  degree 
of  destruction.  The  sense  of  taste  may  likewise  be  lost, 
not  only  in  the  anterior  two-thirds  of  the  tongue,  but 
also  in  the  posterior  third  as  well.  Besides,  the  sense 
of  hearing  is  also  greatly  impaired. 

The  explanation  of  these  changes  is  not  an  easy  one. 
Some  authorities  regard  them  as  due  to  disturbance  of 
trophic  influences.  The  nerve-fibres  which  form  the  pos- 
terior or  sensory  root  of  the  fifth  pair  in  passing  through 
the  Gasserian  ganglion  are  reinforced  by  fibres  which  have 


NERVOUS  FUNCTIONS.  287 

their  origin  in  this  collection  of  nerve-cells.  Each  of 
the  three  divisions  of  the  trigeminus  contains,  therefore, 
fibres  of  the  posterior  root,  and  in  addition  fibres  from 
the  ganglion.  The  latter  fibres  are  distributed  to  the 
structures  to  which  the  sensory  fibres  are  distributed, 
and  they  are  regarded  as  trophic  nerves ;  that  is,  as 
nerves  which  regulate  the  nutrition  of  the  parts  to  which 
they  go.  Among  these  parts  are  the  mucous  membrane 
of  the  nose,  the  cornea,  the  conjunctiva,  and  the  mucous 
membrane  of  the  tongue,  and  the  loss  of  the  special  senses 
is  believed  to  be  due  to  altered  nutrition  of  the  affected 
parts.  The  sense  of  sight  is  resident  in  the  retina  and 
optic  nerve,  but  it  may  be  as  perfectly  abolished  by  ren- 
dering opaque  the  tissues  through  which  light  reaches 
these  structures  as  by  dividing  the  optic  nerve.  In  like 
manner  the  olfactory  nerves  are  the  nerves  of  smell,  but 
if  the  nasal  mucous  membrane  be  so  affected  in  its  nutri- 
tion as  to  render  the  functions  of  these  nerves  impossi- 
ble, the  sense  of  smell  is  as  certainly  abolished  as  if  the 
olfactory  bulb  were  broken  up.  This  interference  with 
the  normal  action  of  the  nerves  is  seen  in  catarrhal  affec- 
tions of  the  nose,  in  which  the  sense  of  smell  is  much 
obtunded  and  sometimes  even  lost. 

Some  authorities,  however,  question  the  influence  of 
so-called  "  trophic  centres "  except  for  nerves.  They 
state  that  the  inflammatory  changes  occurring  in  the 
eye,  for  instance,  are  due  to  the  presence  of  foreign 
bodies  lodging  on  the  eyeball,  which  has  lost  its  sensi- 
bility; that  if  the  eye  be  so  protected  that  irritating  sub- 
stances cannot  injure  it,  the  degenerative  changes  take 
place  only  after  a  considerable  time ;  and  that  when 
they  do  occur  it  is  probably  even  then  due  to  injury,  for 
it  is  a  most  difficult  thing  to  protect  the  eye  for  a  long 


288  HUMAN  PHYSIOLOGY. 

time  from  all  sources  of  irritation.  Similar  reasoning, 
it  is  claimed,  excludes  other  so-called  "trophic  changes." 
It  is,  of  course,  a  mooted  question,  but  it  seems  to  the 
writer  that  no  explanation  of  the  nutritive  changes  taking 
place  after  section  of  the  trigeminus  more  satisfactorily 
accounts  for  them  than  that  which  regards  the  Gasserian 
ganglion  as  a  trophic  centre. 

Ganglia  of  the  Trigeminus. — Besides  the  Gasserian 
ganglion,  there  are,  in  connection  with  the  fifth  nerve, 
four  ganglia  which  are  by  some  writers  described  as 
a  part  of  the  sympathetic  system.  They  are  the  ciliary 
or  ophthalmic,  the  spheno-palatine  or  Meckel's,  the 
otic  or  Arnold's,  and  the  submaxillary. 

The  ciliary  ganglion  belongs,  according  to  some  au- 
thorities, to  the  third  rather  than  to  the  fifth  nerve.  It 
is  not  larger  than  the  head  of  an  ordinary  pin,  and  is 
situated  in  the  orbit.  The  branches  by  which  other 
nerves  communicate  with  it  are  called  its  "  roots ;"  of 
these  there  are  three :  the  sensory,  from  the  ophthalmic 
division  of  the  fifth ;  the  motor,  from  the  motor  oculi ; 
and  the  syjnpathetic ,  from  the  cavernous  plexus  of  the 
sympathetic.  The  nerves  that  go  off  from  it  are  the 
short  ciliary  nerves,  which,  joining  with  the  long  ciliary 
nerves,  form  the  nasal  branch  of  the  ophthalmic  division, 
and  together  they  are  distributed  to  the  ciliary  muscles, 
the  iris,  and  the  cornea.  These  nerves  supply  motor  in- 
fluences to  the  sphincter  and  dilator  pupillse,  sensibility 
to  the  iris,  choroid,  and  sclerotic,  and  vaso-motor  influ- 
ences to  the  blood-vessels  of  the  iris,  choroid,  and  retina. 
If  the  trophic  influence  already  spoken  of  exist,  it  must 
be  conveyed  to  the  eye  through  the  ciliary  nerves. 

T/ie  Spheno-palatine  or  Meckel's  ganglion,  which  is  the 
largest  of  the  four,  is  situated  in  the  spheno-maxillary 


NERVOUS  FUNCTIONS.  289 

fossa.  This  ganglion  also  has  three  roots  :  the  sensory, 
spheno-palatine,  from  the  superior  maxillary  division  of 
the  fifth ;  the  motor,  large  superficial  petrosal  nerve  from 
the  facial ;  and  the  sympathetic,  large  deep  petrosal  nerve 
from  the  carotid  plexus  of  the  sympathetic.  The  Vidian 
nerve  is  made  by  the  union  of  these  two  latter  nerves.  The 
nerves  from  this  ganglion  are  distributed  to  the  posterior 
portion  of  the  nasal  passages  and  the  hard  and  soft  palate, 
giving  them  sensibility ;  to  the  levator  palati  and  azygos 
uvulae,  giving  them  the  power  of  motion ;  and  to  the 
blood-vessels  of  this  region. 

The  Otic  or  Arnold's  ga)iglion  is  situated  on  the  inner 
side  of  the  inferior  maxillary  division  of  the  fifth,  just  below 
the  foramen  ovale.  It  likewise  has  three  roots  :  the  sen- 
sory, from  the  inferior  maxillary  and  glosso-pharyngeal ; 
the  motor,  from  the  facial  and  inferior  maxillary ;  and  the 
sympathetic,  from  the  plexus  around  the  middle  menin- 
geal artery.  Its  branches  of  distribution  are  to  the  tensor 
tympani,  the  tensor  palati,  and  a  small  one  to  the  chorda 
tympani.  The  mucous  membrane  of  the  tympanum  and 
the  Eustachian  tube  is  also  supplied  by  this  ganglion. 

The  submaxillary  ganglion,  which  is  situated  near  the 
submaxillary  gland,  receives  branches  of  communication 
from  the  lingual  branch  of  the  fifth,  chorda  tympani, 
and  sympathetic  plexus  around  the  facial  artery.  Its 
branches  of  distribution  are  to  the  mucous  membrane 
of  the  mouth  and  Wharton's  duct,  also  to  the  submaxil- 
lary gland. 

6.  Abducens. — This  nerve,  which  has  its  real  origin 
in  the  floor  of  the  fourth  ventricle,  escapes  from  the 
cranium  by  the  sphenoidal  fissure,  being  distributed  to 
the  external  rectus  muscle.  It  is  purely  a  motor  nerve, 
as  is  shown  by  the  contraction  of  this  muscle  when  the 

19 


290  HUMAN  PH  YSIOL  OGY. 

nerve  is  stimulated,  and  by  its  paralysis  when  the  nerve 
is  divided. 

Paralysis  of  tJie  Abdiicens. — When  from  any  cause  this 
nerve  is  so  injured  as  to  deprive  it  of  its  function,  the 
internal  rectus,  having  lost  its  antagonist  the  external 
rectus,  turns  the  eye  inward  toward  the  nose,  producing 
internal  strabismus.  There  may  also  be  some  contrac- 
tion of  the  pupil,  because  the  radiating  fibres  of  the  iris, 
which  cause  dilatation  of  the  pupil,  are  to  a  certain  extent 
deprived  of  their  innervation,  this  being  supplied  from 
the  sympathetic,  some  of  the  nerves  of  which  system 
run  along  with  the  abducens,  and  when  this  nerve  is 
injured  these  sympathetic  fibres  may  also  be  involved. 
It  is  said  that  this  nerve  is  more  frequently  implicated  in 
fractures  at  the  base  of  the  skull  than  any  other  cranial 
nerve. 

7.  Facial  Nerve. — The  facial  nerve  leaves  the  medulla 
oblongata  at  the  groove  between  the  olivary  and  restiform 
bodies.  Its  real  origin  is  a  nucleus  on  the  floor  of  the 
fourth  ventricle.  It  leaves  the  cranium  by  the  internal 
auditory  meatus,  through  which  and  the  aqueduct  of 
Fallopius  it  passes  to  emerge  at  the  stylo-mastoid  fora- 
men. In  the  older  nomenclature  it  was  associated  with 
the  auditory  nerve,  in  company  with  which  it  enters  the 
auditory  meatus,  the  facial,  from  its  firm  consistency, 
being  called  the  portio  dura,  and  the  auditory,  on  account 
of  its  opposite  quality,  being  called  the  portio  mollis. 

The  facial  has  a  very  extensive  distribution — the  mus- 
cles of  the  face  and  external  ear,  the  stylo-hyoid,  poste- 
rior belly  of  the  digastric,  the  platysma  myoides,  and  the 
stapedius.  It  also  gives  off  the  chorda  tympani,  which 
is  distributed  to  the  submaxillary  gland  and  ganglion, 
to  the  inferior  lingualis  muscle,  and  to  the  sublingual 


NERVOUS  FUNCTIONS.  29 1 

gland.  Besides  these  it  has  most  important  branches  of 
communication  with  the  sympathetic  system  and  with  the 
glosso-pharyngeal,pneumogastric,  and  trigeminus  nerves. 

Physiological  Properties  of  the  Facial. — The  facial  is, 
originally,  a  purely  motor  nerve,  and  whatever  sensibility 
is  possessed  by  the  parts  to  which  it  is  distributed  is 
not  due  to  facial  fibres,  but  to  anastomotic  fibres  from 
other  nerves,  principally  the  fifth.  The  most  pronounced 
function  of  the  facial  is  its  relation  to  expression.  The 
so-called  "  expression  "  of  the  face  is  caused  by  different 
degrees  of  contraction  of  the  facial  muscles,  and  the 
different  expressions,  such  as  of  fear,  of  anger,  etc.,  are 
due  to  contraction  of  different  muscles.  The  facial  is 
therefore  said  to  be  the  "  nerve  of  expression,"  and  when 
it  is  divided  and  the  muscles  paralyzed  the  reason  for 
this  title  is  readily  understood. 

Facial  Paralysis. — When  the  facial  nerve  is  divided  or 
its  functions  otherwise  abolished  the  following  are  the 
results  : 

(i)  Effect  of  Paralysis  011  Facial  Expression. — A  com- 
plete loss  of  expression  follows  on  the  affected  side ;  the 
wrinkles  on  that  side  are  obliterated  and  the  face  is 
flattened  out. 

(2)  Effect  of  Facial  Paralysis  on  the  Eye. — The  muscle 
which  closes  the  eye  is  the  orbicularis  palpebrarum : 
this  muscle  is  innervated  by  the  facial  nerve,  and  in 
paralysis,  therefore,  the  eye  remains  permanently  open, 
the  power  to  close  it  being  lost.  Inasmuch  as  the  act 
of  winking  is  but  a  rapid  partial  closing  of  the  eye,  this 
act  is  also  abolished  and  the  eyeball  is  liable  to  become 
dry.  The  act  of  winking  spreads  the  tears  which  keep 
the  eye  moi.st.  Unless  provided  against,  this  exposure 
of  the  eye  may  result  in  injury. 


292  HUMAN  PHYSIOLOGY. 

(3)  Effect  of  Facial  Paralysis  on  the  Month. — The  mouth 
is  drawn  by  the  unparalyzed  muscles  to  the  unaffected 
side.  It  is  impossible  to  approximate  the  lips  of  the 
affected  side  to  a  glass ;  consequently,  unless  the  head 
be  thrown  back,  fluids  will  dribble  from  the  corners  of 
the  mouth  in  drinking.  The  buccinator  muscle  being 
paralyzed,  food  finds  its  way  into  the  space  between  the 
cheek  and  the  gum,  and  mastication  is  seriously  im- 
peded. The  lips  being  paralyzed,  the  consonants  b  and 
/  cannot  be  pronounced  distinctly. 

(4)  Effect  of  Facial  Paralysis  on  Taste. — Accompanying 
facial  paralysis  may  be  impairment  or  abolition  of  the 
sense  of  taste.  Authorities  are  not  agreed  as  to  the  ex- 
planation of  this  result,  but  it  is  doubtless  due  to  inter- 
ference with  the  chorda  tympani.  Some  attribute  it  to 
the  influence  which  this  nerve  exercises  over  the  circu- 
lation in  the  tongue  and  on  the  secretion  of  saliva : 
others  regard  the  chorda  tympani  as  the  nerve  of  taste 
to  the  anterior  two-thirds  of  the  tongue,  and  as  taking 
part  in  forming  the  gustatory  nerve  or  lingual  branch 
of  the  trigeminus.  Indeed,  there  is  a  difference  of 
opinion  among  anatomists  as  to  the  true  source  of  the 
chorda  tympani :  some  look  upon  it  as  a  part  of  the  fifth, 
some  as  a  part  of  the  seventh,  and  still  others  as  a  part  of 
the  ninth  or  glosso-pharyngeal,  at  least  so  far  as  concerns 
those  fibres  which  are  connected  with  the  sense  of  taste. 

8.  Auditory. — The  auditory  nerve  has  its  apparent 
origin  from  the  lower  border  of  the  pons,  in  the  groove 
between  the  olivary  and  restiform  bodies.  Its  real  origin 
is  from  the  floor  of  the  fourth  ventricle.  As  already 
stated,  the  auditory  nerve  enters  the  internal  auditory 
meatus  with  the  facial  nerve.  It  is  distributed  to  the 
internal  ear,  and  it  is  the  special  nerve  of  the  sense  of 


NERVOUS  FUNCTIONS.  293 

hearing.  It  will  further  be  discussed  in  connection  with 
that  special  sense. 

9.  Glosso-pharyngeal. — The  superficial  origin  of  the 
glosso-pharyngeal  nerve  is  from  the  upper  part  of  the 
medulla,  in  the  groove  between  the  olivary  and  restiform 
bodies.  Its  real  origin  is  a  nucleus  in  the  lower  part  of 
the  floor  of  the  fourth  ventricle.  It  escapes  from  the 
cranium  through  the  jugular  foramen,  together  with  the 
pneumogastric  and  spinal  accessory  nerves.  Its  branches 
of  communication  are  with  the  pneumogastric,  facial,  and 
sympathetic  nerves.  The  glosso-pharyngeal  gives  off 
the  tympanic  branch,  the  nerve  of  Jacobson,  which  is 
distributed  to  the  fenestra  rotunda,  the  fenestra  ovalis, 
and  the  lining  membrane  of  the  tympanum  and  Eusta- 
chian tube.  As  its  name  implies,  the  glosso-pharyngeal 
is  distributed  to  the  tongue  and  pharynx.  The  glossal 
portion  supplies  the  posterior  third  of  the  tongue,  the 
tonsils,  and  the  mucous  membrane  of  the  pillars  of  the 
fauces  and  the  soft  palate,  while  the  pharyngeal  portion 
is  distributed  to  the  pharyngeal  mucous  membrane  and 
to  the  muscles  concerned  in  a  part  of  the  act  of  deglu- 
tition— namely,  the  styloglossus,  digastric,  and  stylo- 
pharyngeus,  and  the  superior  and  middle  constrictors. 

Physiological  Properties. — The  sensibility  of  the  parts 
to  which  the  glosso-pharyngeal  nerve  is  distributed  is 
due  to  this  nerve.  It  is  also  a  nerve  of  special  sense, 
supplying  the  posterior  third  of  the  tongue  and  the 
palate  with  the  sense  of  taste ;  and,  finally,  it  is  the 
motor  nerve  for  the  muscles  enumerated  which  are  con- 
cerned in  passing  the  food  from  the  back  of  the  mouth 
into  and  through  the  pharynx  to  the  oesophagus  in  the 
act  of  deglutition. 

10.  Pneumogastric. — This  nerve  is  also  called  "  ner- 


294 


HUMAN  PHYSIOLOGY. 


M/W*^^  '\£^^i^^mcii  immm^sii 

Fig.  62. — View  of  the  Nerves  of  the  Eighth  Pair,  their  distribution  and  connections  on 
the  left  side:  i,  pneumogastric  nerve  in  the  neck;  2,  ganglion  of  its  trunk;  3, 
its  union  with  the  spinal  accessory;  4,  its  union  with  the  hypoglossal  ;  5,  pharyngeal 
branch;  6,  superior  laryngeal  nerve;  7,  external  laryngeal;  8  laryngeal  plexus;  9, 
inferior  or  recurrent  laryngeal;  10,  superior  cardiac  branch;  11,  middle  cardiac; 
12,  plexiform  part  of  the  nerve  in  the  thorax;  13,  posterior  pulmonarjr  plexus ;  14, 
lingual  or  gustatory  nerve  of  the  inferior  maxillary;  15,  hypoglossal,  passing  into  the 
muscles  of  the  tongue,  giving  its  thyro-hyoid  branch,  and  uniting  with  twigs  of  the 


NERVOUS  FUNCTIONS.  295 

vus  vagus "  and  "  par  vagum."  Its  common  name  is 
derived  from  two  of  the  important  organs,  the  lungs  and 
stomach,  to  which  it  is  distributed.  Its  apparent  origin 
is  by  eight  or  ten  filaments  from  the  groove  below  the 
glosso-pharyngeal,  while  its  deep  origin  is  from  a  nucleus 
in  the  floor  of  the  fourth  ventricle,  below  and  continuous 
with  that  of  the  same  nerve. 

At  the  jugular  foramen,  by  which  it  escapes  from  the 
cranium,  is  found  the  ganglion  of  the  pneumogastric 
or  the  jugular  ganglion.  The  pneumogastric  receives 
branches  from  the  spinal  accessory,  facial,  hypoglossal, 
and  anterior  branches  of  the  first-  and  second  cervi- 
cal nerves.  It  assists  in  forming  the  pharyngeal,  lar- 
yngeal, pulmonary,  and  oesophageal  plexuses.  Among 
its  important  branches  are  the  superior  and  inferior  lar- 
yngeal nerves,  the  cardiac  and  the  gastric  branches.  The 
pharyngeal  branch  is  distributed  to  the  mucous  mem- 
brane and  muscles  of  the  pharynx  and  to  the  muscles 
of  the  soft  palate.  Its  oesophageal  branches  supply  the 
mucous  membrane  and  muscular  coat  of  the  oesopha- 
gus, so  that  the  act  of  deglutition,  which  begins  in  the 
mouth  and  is  continued  in  the  pharynx,  is  completed 
by  the  oesophagus.  The  superior  laryngeal  nerve  is  dis- 
tributed to  the  crico-thyroid  muscle  and  to  the  inferior 
constrictor,  and  it  communicates  with  the  superior  cardiac 
nerve.  Its  further  distribution  is  to  the  mucous  membrane 
of  the  larynx  and  epiglottis  as  far  as  the  vocal  cords. 

lingual;  16,  glosso-pharyngeal  nerve;  17,  spinal  accessory  nerve,  uniting  by  its  inner 
branch  with  the  pneumogastric,  and  by  its  outer  passing  into  the  sterno-mastoid 
muscle;  i8,  second  cervical  nerve;  19,  third;  20,  fourth;  21,  origin  of  the  phrenic 
nerve;  22,  23,  fifth,  sixth,  seventh,  and  eighth  cervical  nerves,  forming  with  the  first 
dorsal  the  brachial  plexus;  24,  superior  cervical  ganglion  of  the  sympathetic;  25, 
middle  cervical  ganglion;  26,  inferior  cervical  ganglion  united  with  the  first  dorsal 
ganglion;  27,  28,  29,  30,  second,  third,  fourth,  and  fifth  dorsal  ganglia  (from  Sappey 
after  Hirschfeld  and  Leveille). 


296  HUMAN  PHYSIOLOGY. 

The  superior  laryngeal  nerve  is  the  sensitive  nerve 
of  the  larynx.  This  sensibility  is  of  great  import- 
ance as  a  protection  of  the  larynx  and  the  respira- 
tory organs  below  it  from  the  entrance  of  foreign  bodies, 
which  would  set  up  dangerous  inflammatory  processes. 
The  instant  such  a  substance  touches  the  surfaces  sup- 
plied by  this  nerve  a  violent  expulsive  cough  occurs 
which  ejects  it.  If  the  nerve  be  paralyzed,  as  it  may  be 
after  diphtheria  or  in  connection  with  brain  disease,  this 
protection  is  absent,  and,  owing  to  paralysis  of  the  crico- 
thyroid, the  ability  to  make  tense  the  vocal  cords  is  lost 
and  the  voice  is  hoarse. 

The  inferior  or  recurrent  laryngeal  nerve  is  distributed 
to  all  the  muscles  of  the  larynx  except  the  crico-thyroid. 
It  sends  branches  to  the  mucous  membrane  and  muscu- 
lar coat  of  the  oesophagus,  to  similar  structures  of  the 
trachea,  and  to  the  inferior  constrictor.  It  is  the 
motor  nerve  of  the  larynx.  This  nerve  may  be  para- 
lyzed under  the  same  conditions  as  were  mentioned  in 
connection  with  the  superior  laryngeal,  and  all  motion 
of  the  vocal  cords  is  abolished.  One  nerve  might  be 
paralyzed,  as  when  pressed  upon  by  a  tumor,  when  the 
corresponding  vocal  cord  would  alone  be  motionless. 

The  cardiac  branches  of  the  pneumogastric  terminate 
in  the  superficial  and  deep  cardiac  plexuses.  The  pul- 
monary branches  assist  in  forming  the  pulmonary  plex- 
uses whose  branches  are  distributed  to  the  lungs.  The 
oesophageal  branches  form  the  oesophageal  plexus  or 
plexus  gulae.  The  gastric  branches,  which  are  the  ter- 
minal filaments  of  the  nerve,  are  distributed  to  the 
stomach  and  to  the  coeliac,  splenic,  and  hepatic  plex- 
uses, the  latter  two  supplying  the  liver  and  spleen. 

In  mentioning  some  of  the  branches  of  the  pneumo- 


NERVOUS  FUNCTIONS.  297 

gastric  their  functions  have  also  been  referred  to.  In  ad- 
dition to  these  functions  the  movements  of  the  stomach 
and  the  intestines  are  also  performed  under  the  influence 
of  this  nerve.  It  is  through  the  cardiac  branches  that 
the  inhibitory  impulses  from  the  medulla  are  sent  to 
the  heart.  Through  the  pulmonary  branches  impulses 
reach  the  respiratory  centre  and  influence  respiration. 
Reference  has  previously  been  made  to  the  depressor 
fibres,  which  run  in  the  pneumogastric  to  the  vaso- 
motor centre,  inhibiting  its  action  and  thus  diminishing 
the  work  of  the  heart. 

11.  Spinal  Accessory  Nerve. — This  nerve  has  two 
parts — one  arising  from  a  nucleus  in  the  medulla  below 
that  of  the  pneumogastric,  and  the  other  from  the  in- 
termedio-lateral  tract  of  the  cord.  The  former  is  the 
accessory,  and  the  latter  the  spinal,  portion.  The  acces- 
sory portion  joins  the  pneumogastric,  and  it  is  distrib- 
uted through  the  pharyngeal  and  superior  laryngeal 
branches  of  that  nerve.  It  is  also  probable  that  the 
fibres  of  the  pharyngeal  branch  going  to  the  muscles 
of  the  soft  palate  are  fibres  of  this  portion  of  the  spinal 
accessory. 

The  inferior  laryngeal  nerve  also  contains  fibres  from 
this  nerve,  probably  from  the  internal,  anastomotic,  or 
accessory  portion,  and  experiments  demonstrate  that 
the  power  which  the  larynx  possesses  to  produce  vocal 
sounds  is  due  to  these  fibres,  for  when  the  spinal  acces- 
sory is  torn  out  this  power  is  lost.  The  other  move- 
ments of  the  larynx,  those  which  take  place  during 
respiration,  are  not  interfered  with  under  these  circum- 
stances, but  only  those  of  phonation.  The  inferior  lar- 
yngeal nerve  is,  then,  only  partially  made  up  of  spinal 
accessory  fibres :    these  fibres  preside  over  phonation. 


298  HUMAN  PHYSIOLOGY. 

The  Other  fibres,  which  are  probably  derived  from  the 
facial,  hypoglossal,  or  cervical,  or  all  of  them,  provide 
the  nervous  influence  for  the  other  movements.  If  the 
entire  nerve  be  divided,  movements  both  of  phonation 
and  of  respiration  will  cease. 

The  spinal  or  external  portion  is  distributed  to  the 
trapezius  and  sterno-mastoid  muscles ;  it  is  therefore 
sometimes  called  the  "  muscular  branch."  This  branch 
is  believed  to  be  brought  into  requisition  when  these 
muscles  are  needed  for  more  than  their  ordinary  activity, 
for  the  nervous  force  to  supply  the  latter  is  furnished  by 
cervical  nerves.  In  unusual  straining  or  in  lifting  or  in 
the  production  of  prolonged  cries,  these  muscles  are 
brought  into  requisition,  and  to  supply  the  additional 
innervation  which  these  acts  seem  to  require  is  believed 
to  be  the  office  of  the  muscular  branch  of  the  eleventh 
nerve.  The  spinal  accessory  is,  then,  a  motor  nerve, 
although  some  writers  regard  a  portion  of  the  fibres 
of  the  accessory  part  as  being  sensory. 

12.  Hypog-lossal. — The  apparent  origin  of  this  nerye 
is  by  filaments,  from  ten  to  fifteen  in  number,  from  the 
groove  between  the  pyramidal  and  olivary  bodies :  its 
real  origin  is  in  a  nucleus  in  the  floor  of  the  fourth  ven- 
tricle. It  sends  branches  of  communication  to  the  pneu- 
mogastric,  the  sympathetic,  the  first  and  second  cervical, 
and  the  gustatory.  It  is  distributed  to  the  sterno-hyoid, 
sterno-thyroid,  omo-hyoid,  thyro-hyoid,  styloglossus, 
hyoglossus,  genio-hyoid,  and  genio-hyoglossus  muscles. 
It  is  a  motor  nerve  to  the  tongue,  so  much  so  that  it 
has  been  called  the  "  motor  linguae."  The  niovements 
over  which  it  presides  are  those  concerned  in  mastication 
and  deglutition  and  in  the  production  of  articulate  speech. 
When  this  nerve  is  paralyzed  on  one  side,  the  tongue, 


NERVOUS  FUNCTIONS.  299 

when  protruded,  is  directed  toward  the  paralyzed  side. 
When  both  nerves  are  involved  in  the  paralysis,  all 
motion  of  the  tongue  ceases. 

2.  The  Senses. 

It  is  by  the  senses  that  the  individual  is  brought  into 
relation  with  the  world  outside  him.  The  senses  are 
five  in  number:  (i)  General  sensibility;  (2)  Smell ;  (3) 
Taste;  (4)  Sight;  and  (5)  Hearing. 

1.  General  Sensibility. — This  kind  of  sensibility  is  so 
called  because  it  is  generally  distributed  over  the  entire 
body  in  the  skin,  and  in  those  parts  of  mucous  mem- 
brane adjacent  to  the  skin.  It  is  composed  of  a  variety 
of  sensations  which  are  excited  by  a  variety  of  stimuli, 
but  it  is  still  an  unsettled  question  whether  the  nerves 
which  conduct  the  impulses  that  excite  these  sensations 
are  in  all  instances  the  ordinary  sensory  nerves  of  the 
skin,  or  whether  there  are  special  nerves,  each  one  con- 
ducting only  its  own  special  stimulus.  In  treating  of 
the  subdivisions  of  general  sensibility  this  question  will 
again  be  referred  to. 

Sense  of  Touch. — The  sense  of  touch,  or  tactile  sensibil- 
ity, gives  knowledge  of  such  qualities  as  hardness  or  soft- 
ness, roughness  or  smoothness,  sharpness  or  dulness,  etc. ; 
by  it  we  become  acquainted  with  the  shape  and  consist- 
ency of  objects,  and  are  made  aware  of  the  presence  or 
absence  of  irritating  qualities  in  certain  substances.  The 
pungent  vapors  of  some  gases  excite  in  the  nose  the 
ultimate  fibres  of  distribution  of  the  fifth  pair  of  nerves, 
and  not  those  of  the  first  pair,  and  it  is  incorrect  to 
describe  this  sensation  as  a  smell.  It  is  as  truly  a  tactile 
sensibility  as  when  a  sharp-pointed  instrument  is  brought 
in  contact  with  the  skin.     The  same  is  true  of  pungent 


300  HUMAN  PHYSIOLOGY. 

liquids  applied  to  the  tongue,  which  are  commonly,  but 
erroneously,  said  to  be  tasted. 

Tactile  sensibility  differs  in  different  portions  of  the 
body.  Its  comparative  delicacy  is  determined  by  apply- 
ing the  points  of  a  pair  of  compasses  to  the  surface  of 
the  body :  the  minimum  distance  at  which  they  can  be 
recognized  as  two  points  is  the  measure.  At  the  tip  of 
the  tongue  this  distance  is  i  mm.  If  the  points  be 
brought  nearer  together,  they  give  the  sensation  of  one 
point  only.  At  the  tips  of  the  fingers  it  is  1.5  mm.; 
on  the  cheek  it  is  9.46  mm, ;  and  in  the  middle  of  the 
back  it  is   50.43   mm. 

Sense  of  Pressure. — When  an  object  possessing  consid- 
erable weight  is  laid  upon  the  hand,  there  is  a  sensation 
produced  which  is  that  of  "pressure."  If  an  attempt 
be  made  to  raise  this  object,  there  is  a  consciousness  of 
the  fact  that  to  do  this  muscular  power  must  be  exerted, 
and  this  is  called  "  muscular  sense." 

Sense  of  Temperature. — By  this  sense  the  difference  in 
the  temperature  of  bodies  is  recognized,  and  it  is  a  well- 
known  fact  that  the  various  portions  of  the  body  are  en- 
dowed with  different  degrees  of  sensibility  in  this  regard : 
the  hand  will  bear  a  degree  of  heat  which  would  cause 
great  pain  to  some  other  parts  of  the  body.  The  sense 
of  temperature  and  that  of  touch  are  entirely  distinct,  and 
this  fact  may  readily  be  demonstrated  by  pressing  firmly 
on  a  sensitive  nerve  until  the  part  to  which  it  is  distrib- 
uted is  almost  devoid  of  the  sense  of  touch,  when  it  will 
be  found  that  the  sense  of  temperature  is  unaffected. 
•  Sense  of  Pain. — When  the  stimuli  that  call  out  the 
sense  of  touch  or  of  temperature  are  excessive,  the 
sense  of  pain  is  produced,  and  when  produced  the  other 
sensations  are  abolished ;  thus  when  a  piece  of  iron  very 


NERVOUS  FUNCTIONS. 


301 


much  heated  burns  the  hand  the  sensation  is  the  same  as 
when  the  iron  is  very  cold. 

2.  Sense  of  Smell. — The  olfactory  nerves  are  beyond 
all  doubt  the  channels  by  which  olfactory  impressions 
reach  the  brain  (Fig.  63.)    They  are  nerves  of  the  special 


Fig.  63. — Nerves  of  the  Outer  Walls  of  the  Nasal  Fossse;  i,  network  of  the 
branches  of  the  olfactory  nerve,  descending  upon  the  region  of  the  superior  and 
middle  turbinated  bones ;  2,  external  twig  of  the  ethmoidal  branch  of  the  nasal 
nerves;  3,  sphenopalatine  ganglion;  4,  ramification  of  the  anterior  palatine 
nerves;  5,  posterior,  and  6,  middle,  divisions  of  the  palatine  nerves;  7,  branch 
to  the  region  of  the  inferior  turbinated  bone ;  8,  branch  to  the  region  of  the  superior 
and  middle  turbinated  bones  ;  9,  naso-palatine  branch  to  the  septum  cut  short  (from 
Sappey,  after  Hirschfeld  and  Leveille). 

sense  of  smell.  The  whole  Schneiderian  membrane  is 
not  supplied  with  olfactory  fibres;  hence  only  in  that  part 
where  they  are  present,  the  olfactory  membrane,  does 
the  .sense  of  smell  reside.  The  proof  that  the  function  of 
this  nerve  is  that  of  smell  is  derived  from  experiments  upon 
lower  animals  and  from  observations  upon  man.  Ani- 
mals whose  sense  of  smell  is  very  acute  have  the  olfac- 
tory bulbs  and  tracts  more  highly  developed — that  is, 


302  HUMAN  PHYSIOLOGY. 

the  latter  are  larger— than  in  those  animals  in  which  the 
acuteness  of  the  sense  of  smell  is  not  marked.  If  the 
tracts  be  destroyed,  the  sense  of  smell  is  abolished. 
Although  this  experimental  proof  is  not  applicable  in 
man,  still  there  are  cases  on  record  in  which  an  absence 
of  the  sense  of  smell  during  life  has  been  found  after 
death  to  accompany  an  absence  of  the  olfactory  tracts ; 
and  there  are  cases  also  of  individuals  whose  sense  of 
smell  has  been  seriously  impaired  after  injury  to  the 
tracts. 

During  ordinary  respiration  the  inspired  air  does  not 
pass  over  the  olfactory  membrane,  but  only  over  the 
lower  part  of  the  Schneiderian  membrane,  the  respira- 
tory portion.  Hence  if  odors  be  faint,  they  are  not 
detected,  unless  by  a  strong  inspiration  the  air  is  car- 
ried up  to  and  over  that  portion  to  which  the  olfactory 
nerves  are  distributed.  If  the  nasal  passages  be  closed 
by  a  catarrhal  condition,  the  sense  of  smell  is  obtunded 
or  may  even  be  abolished  temporarily. 

It  is  important  to  distinguish  between  the  sense  of 
smell  and  general  sensibility.  The  latter  will  hereafter 
be  noticed  at  length,  but  for  the  present  it  will  only  be 
referred  to.  The  mucous  membrane  of  the  nose  has,  in 
common  with  other  mucous  membranes  and  the  skin, 
the  power  to  recognize  such  physical  properties  in  objects 
as  consistency,  temperature,  etc.  Thus  if  a  sharp  instru- 
ment were  to  be  brought  in  contact  with  this  membrane, 
it  would  be  recognized  as  sharp,  but  this  recognition  is 
not  due  to  the  excitation  of  the  olfactory  nerves,  but  to 
the  fibres  of  the  trigeminus.  The  mucous  membrane  is 
therefore  supplied  by  two  nerves,  the  olfactory  and  the 
fifth.  One  is  not  liable  to  confound  sharpness  with  odor, 
but  the  irritating  effects  of  certain  substances  are  often 


NERVOUS  FUNCTIONS.  3O3 

confounded  with  the  sense  of  smell,  when,  as  a  matter 
of  fact,  it  is  not  the  olfactory,  but  the  fifth  pair,  which  is 
excited.  Thus  if  acetic  acid  be  brought  in  contact  with 
the  mucous  membrane  of  the  nose,  it  will  excite  the  fibres 
of  the  fifth  pair  and  will  produce  an  irritating  effect,  but 
it  would  be  incorrect  to  say  that  we  smelled  it.  If,  how- 
ever, vinegar  were  substituted  for  the  acetic  acid,  we 
should  have  the  irritating  effect  of  the  acetic  acid  it 
contains,  and  in  addition  the  olfactory  nerves  would  be 
excited  by  the  aromatic  ingredients  which  with  the  acid 
form  vinegar;  and  it  would  therefore  be  correct  to  say 
that  we  smelled  the  vinegar. 

The  acuteness  of  the  sense  of  smell  differs  in  different 
individuals,  but  in  most  it  is  well  marked.  It  has  been 
estimated  that  ygr iFo  o"  *^^  ^  milligramme  of  musk  may 
be  detected  by  this  sense.  The  emanations  from  objects 
which  excite  the  sense  of  smell  produce  this  effect  by 
exciting  the  cells  of  Schultze,  and  the  impulses  are  car- 
ried by  the  olfactory  nerves  to  the  brain, 

3.  Sense  of  Taste. — The  sense  of  taste  resides  not 
only  in  the  tongue,  but  also  in  the  soft  palate,  the  uvula, 
the  pillars  of  the  fauces,  the  tonsils,  and  the  upper  part 
of  the  pharynx.  The  nerve  supplying  the  anterior  two- 
thirds  of  the  tongue  with  this  sense  is  the  lingual  branch 
of  the  fifth  pair,  while  the  posterior  portion  depends  for 
this  power  upon  the  glosso-pharyngeal.  The  relation 
which  the  corda  tympani  bears  to  the  sense  of  taste  has 
been  discussed  in  connection  with  the  facial  nerve,  of 
which  it  is  a  branch. 

It  is  difficult  to  state  exactly  the  difference  in  sensi- 
bility to  sapid  substances  of  the  different  portions  of  the 
tongue,  but  the  most  sensitive  portions  are  the  base,  the 
tip,  and  the  edges  (Fig.  64J :  the  middle  portion  is  less 


304 


HUMAN  PHYSIOLOGY. 


sensitive,  probably  on  account  of  the  greater  thickness  of 
the  epithehum,  while  the  under  surface  is  almost  entirely- 
insensitive. 


Fig.  64. — Papillar  Surface  of  the  Tongue,  with  the  Fauces  and  Tonsils  ;  1,1,  circum- 
vallate  papillae,  in  front  of  2,  the  foramen  ca;cum  ;  3,  fungiform  papillae;  4,  filiform 
and  corneal  papillae;  5,  transverse  and  oblique  rugae;  6,  mucous  glands  at  the  base 
of  the  tongue  and  in  the  fauces;  7,  tonsils;  8,  part  of  the  epiglottis;  9,  median 
glosso-epiglottidean  fold  (frsenum  epiglottidis)  (from  Sappey). 

The  mucous  membrane  of  the  tongue  is  covered  with 
papillae  of  three  varieties — circumvallate,  fungiform,  and 
filiform.    The  circumvallate  papillce,  eight  or  ten  in  num- 


NERVOUS  FUNCTIONS.  305 

ber,  form  the  boundary  between  the  anterior  two-thirds 
and  the  posterior  third  of  the  tongue.  Tliey  are  arranged 
in  V-shape,  the  apex  being  backward.  In  these  papillae 
are  the  gustatory  buds  or  "  taste-goblets,"  which  are  be- 
lieved to  be  connected  with  the  sense  of  taste,  although 
no  connection  of  nerves  with  them  has  been  traced. 
These  bodies  have  also  been  found  at  the  root  of  the 
tongue  and  on  the  posterior  surface  of  the  epiglottis. 
The  fimgiform  papillce  are  especially  abundant  at  the 
sides  and  tip,  and  less  so  on  the  dorsum.  The  filiform 
papillce  are  the  most  numerous  of  all  the  papillae,  and, 
though  present  on  all  portions  of  the  mucous  membrane 
of  the  tongue,  are  very  abundant  on  the  dorsum.  The 
filiform  papillae  are  probably  tactile  organs,  while  the 
other  two  varieties  are  connected  with  the  sense  of  taste. 

The  fact  that  the  general  sensibility  of  the  tongue  may 
be  lost  and  the  sense  of  taste  remain  would  indicate  that 
the  channels  for  the  transmission  of  these  two  sensations 
are  different  It  may  be  well  to  again  call  attention  to 
the  necessity  for  making  a  distinction  between  what  may 
be  tasted  and  what  may  be  smelled,  between  savors  and 
flavors.  The  sense  of  taste  gives  cognizance  of  the  qual- 
ities sweet,  sour,  salty,  etc.,  but  to  speak  of  an  oily  taste 
is  incorrect :  such  a  quality  appeals  to  general  sensi- 
bility only. 

Conditions  of  the  Sense  of  Taste. — That  the  sense  of 
taste  may  be  exercised  requires  the  presence  of  certain 
conditions,  one  of  which  is  that  the  substance  must  be 
in  a  state  of  solution  or  be  soluble  in  the  saliva.  Insol- 
uble sub.stance  are  tasteless :  for  this  reason  calomel  is 
especially  suitable  as  a  cathartic  for  children.  Another 
condition  is  that  the  mucous  membrane  of  the  mouth 
must  be  moist.  When  the  mouth  is  dry  and  substances 
20 


306  HUMAN  PHYSIOLOGY. 

not  already  in  a  state  of  solution  are  taken  in,  there  is  no 
saliva  present  to  dissolve  them  ;  consequently  they  are 
not  tasted.  This  absence  of  taste  is  very  marked  in  the 
parched  condition  of  the  mouth  occurring  during  fevers. 

To  excite  the  sense  of  taste,  sapid  substances  must 
pass  by  osmosis  into  the  papillae  of  the  mucous  mem- 
brane and  there  stimulate  the  terminal  filaments  of  the 
nerves  which  preside  over  this  sense.  An  important 
agent  in  causing  this  absorption  is  the  movement  of  the 
tongue.  It  is  a  matter  of  common  observation  that  if 
sapid  substances  be  simply  placed  on  the  tongue,  the 
sense  of  taste  is  not  excited,  but  if  the  tongue  be  pressed 
against  the  roof  of  the  mouth,  absorption  is  promoted 
and  the  gustatory  qualities  are  at  once  recognized. 

It  is  to  be  noted  also  that  a  savor  persists  for  a  certain 
length  of  time,  and  that  if  it  be  desired  to  determine  the 
comparative  qualities  of  different  substances  by  the  sense 
of  taste,  there  must  either  be  intervals  between  the  tests 
or  something  must  be  used  to  obliterate  the  taste  of  one 
of  the  articles  before  another  is  taken  into  the  mouth. 
It  is  also  noteworthy  that  some  savors  so  powerfully 
impress  the  taste-organs  that  others  fail  to  make  any 
impression.  This  principle  is  made  practical  use  of  in 
rendering  disagreeable  medicines  tasteless.  Thus  a  few 
cloves  eaten  before  taking  a  dose  of  castor  oil  will  render 
the  latter  far  less  nauseous ;  a  mouthful  of  brandy  will 
have  the  same  effect. 

4.  Sense  of  Sight. — The  anatomy  of  the  human  eye 
(Fig.  65)  is  so  complicated  that  only  such  points  as  are 
essential  to  an  understanding  of  some  of  its  more  im- 
portant functions  will  be  referred  to. 

Sclerotic  Coat. — The  sclerotic  coat  is  the  outside  and 
enclosing  membrane  of  the  eyeball,  the  anterior  portion 


NERVOUS  FUNCTIONS. 


307 


being  the  so-called  "  white  of  the  eye."     To  it  are  at- 
tached the  tendons  of  the  muscles  which  move  the  eye- 


SCLCROTIC' 

CHO;«oi> 


lUARv  Pnocesc 

RCULAR    SINUS 


CAAAL  or  pcm 


Fig.  65. — Section  of  Eyeball. 


ball.  In  the  anterior  part  the  membrane  is  absent  and 
its  place  is  occupied  by  the  cornea. 

Cornea. — This  structure  is  the  most  prominent  portion 
of  the  eyeball,  and  by  virtue  of  its  transparency  the  iris 
can  be  seen  through  it. 

Choroid. — Internal  to  the  sclerotic  is  the  choroid, 
a  vascular  membrane  containing  pigment.  Its  ante- 
rior portion  is  thickened,  forming  the  ciliary  body,  the 
inner  parts  of  which  consist  of  folds,  the  ciliary  proc- 
esses. 

Iris. — The  iris  is  a  muscular  curtain  behind  the  cornea, 
the  fibres  being  both  circular  and  radiating  (Fig.  66).  In 
the  centre  is  an  opening,  the  pupil,  around  which,  on  the 
posterior  surface  of  the  iris,  are  arranged  the  circular 
fibres  forming  the  sphincter  pupillae,  which  receives  its 
nervous  supply  from  the  motor  oculi  through  the  ciliary 


3o8 


HU3IAN  PHYSIOLOGY. 


ganglion.  The  muscular  fibres  which  form  the  dilator 
pupillae  are  arranged  in  a  radiating  direction  from  the 
circumference  to  the  margin  of 
the  pupil,  where  they  blend  with 
the  fibres  of  the  sphincter.  These 
fibres  are  supplied  with  sympa- 
thetic nerves  from  the  ciliary 
ganglion.  It  is  the  iris  that 
gives  to  the  eye  its  character- 
istic color,  which  varies  in  dif- 
ferent persons  according  to  the 
amount  and  the  arrangement  of 
the  pigment,  the  latter  being 
more  abundant  and  more  dis- 
seminated in  dark  than  in  light 
eyes. 


Fig.  66. — Choroid  Membrane  and  Iris,  exposed 
by  the  removal  of  the  sclerotic  and  cornea  : 
a,  one  of  the  segments  of  the  sclerotic  thrown 
back  ;  l>,  ciliary  muscle  ;  c,  iris  ;  e,  one  of  the 
ciliary  nerves  ;  /,  one  of  the  vasa  vorticosa 
or  choroidal  veins  (Quain). 


Fig.  67. — Diagrammatic  Section  of 
Retina,  showing  the  relation  of  the 
different  layers  in  the  posterior  part 
of  the  fundus  (not  the  macula  lutea) 
(Schultze):  I,  nerve-fibre  layer  in 
which  the  retinal  vessels  run  next 
to  the  vitreous  humor ;  2,  layer  of 
nerve-cells ;  3,  internal  granular 
layer;  4,  internal  nuclear  layer;  5, 
external  granular  layer  ;  6,  external 
nuclear  layer ;  7,  rods  and  cones 
with  their  extremities  imbedded  in 
the  epithelial  cells;  8,  pigmented 
epithelium  lying  next  to  the  choroid 
coat. 


Ciliary  Muscle. — Between  the   sclerotic  and   choroid, 
anteriorly,  is  the  ciliary  muscle,  a  band  about   3  mm. 


NERVOUS  FUNCTIONS.  3O9 

broad,  composed  of  radiating  and  circular  unstriped 
fibres. 

Retina. — The  retina  is  the  most  internal  of  the  tunics 
of  the  eye,  and  it  is  the  portion  which  receives  the  rays 
of  light.  In  the  centre  of  the  retina  is  the  macula  lutea, 
or  yellow  spot  of  Sommering,  and  at  its  centre  is  a  depres- 
sion, the  fovea  centralis  (Fig.  67).  At  a  distance  of  about 
2.5  mm.  internal  to  the  macula  lutea  is  the  optic  disk,  the 
entrance  of  the  optic  nerve.  As  at  this  point  vision  is 
absent,  it  is  also  called  the  "blind  spot."  Through  its 
centre  passes  the  central  artery  of  the  retina. 

The  structure  of  the  retina  is  very  complex,  being  made 
up  of  ten  layers  : 

(i)  Meinbrana  liinitans  interna,  the  most  internal  layer. 

(2)  Fibrous  layer,  composed  of  nerve-fibres  of  the  optic 
nerve. 

(3)  Vesicular  layer,  consisting  of  large  ganglionic  nerve- 
cells,  one  process  from  each  of  which  passes  into  the  fibrous 
layer,  and  which  is  regarded  as  connecting  with  a  nerve- 
fibre,  while  from  the  other  end  of  the  cell  goes  off  another 
process  (in  some  more  than  one),  which  passes  into 
the  fourth  layer. 

(4)  Inner  molecular  or  granular  layer,  so  called  from 
its  granular  appearance,  consists  of  minute  fibres  which 
are  believed  to  connect  with  the  adjoining  layer. 

(5)  Inner  nuclear  layer,  containing  oval  nuclei  be- 
lieved to  be  bipolar  nerve-cells,  one  process  of  which 
passes  into  the  inner  molecular  layer,  and  which  is 
regarded  by  some  as  connecting,  through  this,  with  the 
ganglion-cells  of  the  third  layer:  the  other  process 
passes  into  the  sixth  layer,  and  is  believed  to  connect 
with  the  rods  and  cones.  Besides  the  oval  nuclei  this 
layer  contains  other  cells. 


3IO  HUMAN  PHYSIOLOGY. 

(6)  Otiier  molecular  layer,  containing  minute  fibres  and 
stellate  cells,  regarded  as  ganglion-cells. 

(7)  Outer  nuclear  layer,  consisting  of  oval  nucleated  cells 
of  two  varieties  ;  one  variety,  called  "  rod-granules,"  con- 
nects with  the  rods  of  the  ninth  layer,  and  the  other, 
called  "  cone-granules,"  connects  with  the  cones  of  that 
layer. 

(8)  Membrana  limitans  externa  is  the  next  layer. 

(9)  Jacob's  membrane,  or  layer  of  rods  and  cones,  is  com- 
posed of  rods  and  cones,  the  former  solid  bodies  arranged 
perpendicularly  to  the  surface,  each  of  which  is  made 
up  of  an  outer  and  an  inner  part  joined  together.  The 
outer  part  presents  a  striated  appearance,  and  is  composed 
of  disks,  one  upon  another.  The  inner  part  connects  with 
a  rod-granule  of  the  seventh  layer.  The  cones,  which 
are  not  so  numerous  as  the  rods,  are  conical  in  shape, 
their  bases  lying  in  the  membrana  limitans  externa. 
They  possess  also  an  inner  and  an  outer  portion,  the 
former  being  likewise  striated,  but  the  latter  is  more 
bulging. 

(10)  Pigmentary  layer,  consisting  of  a  single  layer  of 
pigmented  cells,  was  formerly  regarded  as  belonging  to 
the  choroid. 

The  retina  at  the  macula  lutea  differs  in  structure  from 
that  just  described,  inasmuch  as  the  nerve-fibres  of  the 
second  layer  do  not  form  a  continuous  layer;  the  third 
layer  is  composed  of  several  strata  of  cells  instead  of 
one  stratum ;  there  are  only  cones,  no  rods,  and  in  the 
seventh  layer  there  are  only  cone-granules.  At  the 
fovea  centralis  are  to  be  found  only  the  cones,  the  outer 
nuclear  layer,  and  a  thin  inner  molecular  layer. 

Anterior  and  Posterior  Chambers. — The  anterior  cham- 
ber is  the  space  between  the  cornea  and  the  iris,  while  the 


NERVOUS  FUNCTIONS.  3II 

posterior  chamber  is  the  space  between  the  peripheral 
part  of  the  iris,  the  suspensory  hgament,  and  the  cihary 
processes.  The  latter  is  very  much  smaller  than  it  was 
formerly  supposed  to  be ;  indeed,  it  hardly  deserves  the 
name  of  "  chamber."  Both  these  .spaces  are  filled  with 
aqueous  humor,  an  alkaline  fluid,  96.7  per  cent,  of  which 
is  water  and  o.i  sodium  chloride. 

Vitreous  Body. — This  body  is  composed  of  transpa- 
rent, jelly-like  material,  called  also  "  vitreous  humor," 
which  is   enclosed   by  the   hyaloid  membrane.     In  the 


Fig.  68. — Fundus   of  an    Eye    containing   little   pigment,  choroidal    vessels   visible 
(Wecker). 

anterior  portion,  which  is  depressed,  this  membrane  is 
wanting,  and  in  the  depression  is  the  crystalline  lens. 
The  margin  of  the  hyaloid  membrane  is  attached  to  the 
margin  of  the  lens,  and  it  is  called  the  "suspensory  lig- 
ament." • 

Crystalline  Lens. — The  lens  is  transparent  and  doubly 
convex,  being  more  convex  on  the  posterior  than  on  the 


312 


HUMAN  PHYSIOLOGY. 


anterior  surface.  It  is  situated  behind  the  pupil,  between 
the  aqueous  humor  and  the  vitreous  body,  and  is  sup- 
ported by  these  structures  and  the  suspensory  hgament. 
It  is  contained  in  its  capsule,  which  is  also  transparent 
and  highly  elastic.  The  capsule  is  in  contact  with  the 
border  of  the  iris,  but  not  with  the  rest  of  the  structure, 
and  the  small  space  thus  left  is  the  posterior  chamber. 

Suspefisory  Ligament. — This  ligament  is  a  portion  of 
the  hyaloid  membrane  which  encloses  the  vitreous  body, 
and  is  situated  between  that  body  and  the  ciliary  pro- 
cesses.    It  aids  in  supporting  the  lens. 

Arterial  Supply  to  the  Eye. — The  vessels  which  supply 
blood  to  the  eye  are  the  ciliary  arteries  and  the  arteria  cen- 
tralis retinae  (Figs.  68,  69). 
The    nervous    supply    has 
already  been  considered. 

Physiology  of  Vision. — 
The  eye  has  very  aptly 
been  compared  to  a  photo- 
graphic camera,  the  trans- 
parent structure  through 
which  pass  the  rays  of 
light  representing  the 
lenses,  and  the  retina  rep- 
resenting the  sensitive 
plate  on  which  the  image  is  received,  while  the  pig- 
mented choroid  coat  is  the  representative  of  the  lamp- 
black with  which  the  photographer  darkens  the  interior 
of  the  camera-box  to  prevent  any  reflected  light  striking 
the  plate  and  interfering  with  the  sharpness  of  the  pic- 
ture. In  the  camera,  in  order  to  bring  to  a  focus  upon 
the  plate  the  rays  of  light  coming  from  objects  at  differ- 
ent distances,  the  photographer  uses  a  focusing  screw, 


Fig.  69. — Normal  Optic  Disk  of  the  Left 
Eye  (after  Jaeger). 


NERVOUS   FUNCTIONS.  313 

by  which  the  lens  may  be  moved  nearer  to  or  farther 
from  the  object  he  wishes  to  photograph  ;  and  in  order 
that  clear  images  may  be  obtained  by  the  eye  it  is  neces- 
sary to  accomplish  the  same  result,  for  when  the  eye  is 
focused  for  near  objects  those  at  a  distance  are  blurred, 
and  vice  versa.  This  fact  may  readily  be  demonstrated 
by  looking  through  a  piece  of  mosquito-netting  at  the 
windows  of  a  house  on  the  opposite  side  of  a  street. 
When  the  threads  of  the  net  can  be  seen  distinctly  the 
bars  of  the  window  will  be  indistinct,  and  when  the  bars 
of  the  window  are  clear  and  distinct,  then  the  threads 
are  blurred.  In  the  optical  apparatus  of  the  eye  there 
is  no  provision  for  altering  the  position  of  the  lenses, 
but  there  is  one  which  answers  the  same  purpose,  and 
which  is  called  "  accommodation."  In  connection  with 
every  camera  there  is  an  arrangement  of  openings 
or  diaphragms  by  which  a  greater  or  lesser  amount 
of  light  may  be  admitted  according  to  circumstances. 
In  the  eye  the  iris  serves  a  similar  purpose.  In  many 
cameras  it  is  necessary  to  have  a  number  of  such  dia- 
phragms, each  having  openings  of  different  sizes,  but 
some  are  provided  with  a  single  one,  the  size  of  whose 
opening  can  be  altered ;  this  is  called  an  "  iris  dia- 
phragm," and  is  a  rude  contrivance  compared  with  the 
natural  iris  from  which  it  derives  its  name,  and  which 
by  means  of  its  muscular  fibres  can  alter  in  a  moment 
the  size  of  the  pupil. 

Rays  of  light  coming  from  an  object,  in  order  to  pro- 
duce a  distinct  image  of  that  object,  must  be  brought  to 
a  focus  upon  the  retina.  If  the  media  through  which 
the  light  from  an  object  passes  to  reach  the  retina  were 
all  of  the  same  density  as  the  air,  and  were  also  plane 
surfaces,  an  impression  would  be  produced,  but  there 


314  HUMAN  PHYSIOLOGY. 

would  be  no  distinct  image.  Actually,  before  such 
rays  do  reach  the  retina,  they  must  pass  through  certain 
media  which,  by   reason    of  both    density  and  shape. 


Fig.  70. — Principal  Focus  of  a  Convex  Lens.  The  parallel  rays,  a,  b,  c,  d,  are  re- 
fracted by  the  lens  so  as  to  unite  at  the  point  F,  on  the  axis,  P ;  the  ray,  P,  under- 
goes no  refraction.     F  is  the  principal  focus. 

refract  them  and  bring  them  to  a  focus,  thus  producing 
a  sharp  and  distinct  image  of  the  object  looked  at. 
These  media  are  the  cornea,  the  aqueous  humor,  the 
crystalline  lens,  and  the  vitreous  body.  The  cornea  by 
its  density  and  convex  shape  refracts  the  rays  falling 
upon  it,  but,  as  its  anterior  and  posterior  surfaces 
are  parallel,  the  cornea  and  the  aqueous  humor 
may  be  considered  together  as  one  medium,  the 
posterior  surface  of  which,  that  of  the  aqueous  humor 
covering  the  convex  crystalline  lens,  is  concave.  The 
anterior  convex  surface  of  the  cornea  and  the  concave 
posterior  surface  of  the  aqueous  humor  act  as  a  con- 
cavo-convex lens,  so  that  there  are  in  reality  but  three 
media:  i,  cornea  and  aqueous  humor;  2,  crystalline 
lens;  and  3,  vitreous  body.  The  optical  axis  of  the  eye 
passes  through  the  centre  of  the  cornea,  directly  back- 
ward through  all  these  media  until  it  terminates  in  the 
fovea  centralis  of  the  retina.  Rays  of  light  falling  upon  the 
cornea  are  refracted  and  made  convergent,  and  this  effect 
is  increased  by  the  lens,  so  that  when  the  rays  reach  the 


NERVOUS  FUNCTIONS. 


315 


retina  they  are  brought  to  a  focus.  If  the  entire  optical 
apparatus  of  the  eye  were  rigid  and  immovable,  it  would 
be  necessary,  in  order  to  obtain  a  clear  image  of  an  object, 
either  for  the  individual  to  approach  or  to  recede  from 
the  object,  or  to  cause  the  object  to  do  the  same  with 
reference  to  him,  for  only  parallel  rays — namely,  rays 
coming  from  objects  at  a  distance  of  10  metres  or  more 
— are  brought  to  a  focus  in  the  normal  eye  unless  some 
change  is  brought  about  in  the  refractive  media.  If  an 
object  be  within  that  distance,  the  rays  of  light  coming 
from  it  are  brought  to  a  focus  by  altering  the  shape  of 
the  crystalline  lens  ;  this  is  accommodation. 

Acco7nniodation. — As  already  stated,  the  optical  appa- 
ratus of  the  eye  is  .in  a  state  of  rest  when  it  is  looking 
at  objects  more  than  10  metres  away;  thus  to  see  the 
stars,  although  millions  of  kilometres  distant,  no  effort  is 


Fig.  71.— Diagram  showing  the  Changes  in  the  Lens  during  Accommodation.  The 
cih'ary  muscle  on  the  right  is  supposed  to  be  passive,  as  in  looking  at  distant  objects : 
the  suspensory  ligament,  L,  is  therefore  tight,  and  compresses  the  anterior  surface  of 
the  lens,  W,  so  as  to  flatten  it.  On  the  left  the  ciliary  muscle,  M,  is  contracting, 
so  as  to  relax  the  ligament,  which  allows  the  lens  to  become  more  convex.  This 
contraction  occurs  when  looking  at  near  objects. 


required ;  but  if  it  be  desired  to  see  objects  within  that 
distance,  there  is  a  change  in  the  refractive  media  until 
a  point  so  close  to  the  eye  is  reached  that  no  amount  of 
effort  will  enable  them  to  be  seen.  The  point  at  which 
objects  cease  to  be  seen  distinctly  is  called  the  "  near 


3i6 


HUMAN  PHYSIOLOGY. 


point,"  and  it  is,  for  a  normal  or  emmetropic  eye,  about 
12  cm.,  although  it  is  not  the  same  in  all  persons. 

The  accommodation  of  the  eye  is  brought  about 
especially  by  the  change  in  the  shape  of  the  crystalline 
lens ;  thus  in  looking  at  near  objects  the  eye  becomes 
more  convex.  This  accommodation  is  accomplished  in 
the  following  manner :  The  lens  is  a  very  elastic  struc- 
ture, which  is  kept  in  a  less  convex  condition  when  far 


Fig.  72. 


Fig,  73. 

Fig.  72. — Diagram  showing  three  reflections  of  a  candle  :  i,  from  the  anterior  surface 
of  cornea ;  2,  from  the  anterior  surface  of  lens ;  3,  from  the  posterior  surface  of  lens. 
For  further  explanation  see  text.  The  experiment  is  best  performed  by  employing 
an  instrument  invented  by  Helmholtz,  termed  a.j>hakoscope. 

Fig.  73.^Phakoscope  of  Helmholtz  :  a.t  B  B'  are  two  prisms,  by  which  the  light  of 
a  candle  is  concentrated  on  the  eye  of  the  person  experimented  with;  A  is  the 
aperture  for  the  eye  of  the  observer.  The  observer  notices  three  double  images,  as 
in  Fig.  72,  reflected  from  the  eye  under  examination  when  the  eye  is  fixed  upon  a 
distant  object;  the  position  of  the  images  having  been  noticed,  the  eye  is  then  made 
to  focus  a  near  object,  such  as  a  reed  pushed  up  ;  the  images  from  the  anterior 
surfaces  of  the  lens  will  be  observed  to  move  toward  each  other,  in  consequence 
of  the  lens  becoming  more  convex. 

objects  are  looked  at  than  its  elasticity  would  cause  it 
to  assume  were  it  allowed  free  play ;  but  the  lens  is 
enclosed  in  a  capsule  to  which  the  suspensory  ligament 


NERVOUS  FUNCTIONS.  317 

is  attached,  and  the  tension  of  this  Hgament  is  such  as 
to  pull  upon  the  anterior  portion  of  the  capsule  and 
flatten  it,  at  the  same  time  flattening  the  anterior  sur- 
face of  the  contained  lens.  But  when  a  near  object  is 
to  be  looked  at,  the  ciliary  muscle  contracts,  and  as  its 
fixed  point  is  at  the  junction  of  the  cornea  and  sclerotic, 
this  contraction  draws  the  ciliary  processes  forward  and 
relaxes  the  suspensory  ligament,  thus  removing  the 
influence  which  tends  to  flatten  the  lens  and  permits 
the  latter  by  its  elasticity  to  become  more  convex.  The 
act  is  a  voluntary  one,  the  nervous  supply  for  which  is 
furnished  to  the  ciliary  muscle  by  the  motor  oculi 
through  the  ciliary  nerves.  At  the  same  time  that  this 
muscular  action  is  taking  place  the  pupil  becomes  smaller 
and  the  eyes  converge. 

Pliakoscope  of  Hcbnholtz. — The  above  explanation  of 
the  mechanism  of  accommodation  is  attributable  to 
Helmholtz,  who,  to  demonstrate  it,  has  devised  an  ap- 
paratus called  a  "  phakoscope "  (Fig.  73),  but  it  may 
also  be  demonstrated  in  the  following  manner :  If  a 
candle-flame  be  held  at  one  side  of  the  eye  of  a  person 
who  is  looking  at  a  distant  object,  and  an  observer 
look  at  the  other  side,  he  will  see  three  images  of  the 
flame,  the  brightest  and  most  distinct  being  an  erect 
image  which  is  formed  by  the  anterior  surface  of  the 
cornea.  Besides  this  image  there  is  a  second  image, 
which  is  also  erect,  but  which  is  less  distinct  and  larger; 
this  image  is  formed  at  the  anterior  surface  of  the  lens. 
A  third  image  is  also  seen,  which  is  inverted  and  also 
indistinct;  this  image  is  formed  at  the  posterior  surface 
of  the  lens,  which,  being  concave  forward,  acts  like  a 
concave  mirror  and  inverts  the  image.  If  the  person 
then  look  at  a  near  object,  the  second  image  becomes 


3l8  HUMAN  PHYSIOLOGY. 

brighter  and  smaller,  and  at  the  same  time  approaches 
the  first,  while  the  first  image  undergoes  no  change,  and 
the  third  a  change  so  slight  as  not  to  be  perceptible 
(Fig.  72).  This  proves  that  in  accommodating  the  eye 
for  near  objects  the  change  which  takes  place  is  an 
increase  in  the  convexity  of  the  anterior  surface  of  the 
crystalline  lens.  The  same  may  be  shown  by  looking 
at  the  eye  from  the  side,  when  in  accommodation  the 
iris  may  be  seen  to  move  forward,  being  pushed  in  that 
direction  b}^  the  anterior  surface  of  the  lens  with  which 
it  is  in  contact. 

Emnietropia  is  a  condition  of  the  eye  in  which  the 
principal  focus  falls  exactly  upon  the  layer  of  rods  and 
cones  of  the  retina  when  the  accommodation  is  relaxed, 
or,  as  it  is  expressed,  when  the  eye  is  in  a  state  of  accom- 
modative rest.  This  is  another  way  of  saying  that  in 
this  condition  of  the  eye  parallel  rays  are  focused  on  the 
retina.     An  emmetropic  eye  is  a  normal  eye. 

Ametropia. — Whenever  the  permanent  condition  of  an 
eye  is  not  as  described  above  it  is  one  of  ametropia.  Of 
this  condition  there  are  several  varieties. 

Myopia. — A  myopic  eye  is  one  that  is  abnormally 
elongated,  and  some  authorities  regard  an  increased 
convexity  of  the  lens  as  constituting  an  essential  part  of 
this  condition.  The  retina  is  so  far  from  the  lens  that 
parallel  rays  are  focused  in  front  of  it,  and,  crossing,  do 
not  form  distinct  images  on  the  retina,  the  images  being 
blurred.  To  correct  this,  concave  glasses  are  used,  which 
cause  these  rays  to  diverge  as  they  enter  the  eye,  and  by 
adjusting  the  concavity  to  the  amount  of  myopia  parallel 
rays  are  thus  brought  to  a  focus  on  the  retina  as  they 
are  in  the  emmetropic  eye  without  glasses.  A  myopic 
eye  is  commonly  said  to  be  a  "  near-sighted  "  one. 


NERVOUS  FUNCTIONS.  319 

Hypcrmetropia. — In  this  condition  the  eye  is  shorter 
than  normal,  and  the  retina  is  too  near  the  lens,  so  that 
parallel  rays  are  brought  to  a  focus  behind  the  retina  and 
indistinct  vision  is  produced,  as  in  the  myopic  eye.  In  the 
endeavor  to  overcome  this  defect  the  ciliary  muscle  is  liable 
to  overstrain  in  order  to  converge  the  rays  to  a  focus  upon 
the  retina,  and  the  constant  effort  is  painful  and  injurious. 
The  condition  is  corrected  by  the  use  of  convex  glasses. 

Presbyopia,  which  is  sometimes  called  "  old  sight," 
sometimes  "  long  sight,"  is  the  condition  of  the  eye  seen 
in  elderly  people.  In  this  condition  it  is  difficult  to  see 
near  objects,  although  the  vision  for  those  at  a  distance 
is  unaffected.  It  is  usually  attributed  to  a  lessened  elas- 
ticity of  the  lens,  though  the  ciliary  muscle  is  also  less 
strong,  and  some  writers  state  that  it  depends  on  dimi- 
nution of  the  convexity  of  the  cornea.  To  aid  in  correct- 
ing it  convex  glasses  are  used. 

Astigmatism. — In  this  condition  the  cornea  is  usually 
at  fault,  its  curvature  being  greater  in  one  meridian  than 
in  another,  and  consequently  the  rays  of  light  from  an 
object  are  not  all  brought  to  the  same  focus,  and  the 
image,  therefore,  is  not  distinct.  For  the  correction  of 
astigmatism  glasses  are  worn  which  are  segments  of  a 
cylinder — that  is,  curved  in  but  one  direction — and  which 
are  known  as  "  cylindrical "  glasses.  The  crystalline 
lens  may  also  be  at  fault  in  astigmatism. 

Functions  of  the  Retina. — As  odors  excite  the  olfactory 
apparatus  and  savors  excite  the  gustatory,  so  does  light 
excite  the  retina.  As  neither  odors  nor  savors  reach  the 
brain,  where  smell  and  taste  are  produced,  but  only  the 
nerve-impulses  which  they  excite  and  which  the  olfac- 
tory and  gustatory  nerves  transmit,  so  when  the  light- 
waves fall  upon  the  retina  they  go  no  farther ;  but  the 


320  HUMAN  PHYSIOLOGY. 

nerve-impulses  which  they  there  excite  are  carried  to 
the  brain  by  the  optic  nerve  and  produce  the  sensation 
called  "  light."  Thus  it  is  that  a  blow  upon  the  eye  or 
an  injury  to  the  optic  nerve  produces  in  the  brain  the 
impression  of  a  flash  of  light,  although  the  room  in  which 
the  blow  or  injury  was  received  may  be  absolutely  dark. 
That  the  optic  nerve  is  itself  insensitive  to  light  is 
shown  by  the  fact  that  at  the  point  where  it  enters  the 
eye,  forming  the  optic  disk,  is  the  "  blind  spot,"  at  which 
there  is  an  entire  absence  of  sight.  This  fact  may  be 
demonstrated  in  the  following  simple  way :  Look  with 
the  right  eye  at  the  round  black  spot  here  printed, 


closing  the  left  eye,  and  holding  the  book  six  inches  from 
it.  The  spot  and  the  cross  can  both  be  seen.  Now 
carry  the  book  away  from  the  face  farther  and  farther, 
still  looking  at  the  spot.  A  point  will  be  reached  where 
the  cross  will  all  at  once  disappear,  and  when  this  occurs 
the  light  from  the  cross  falls  upon  the  optic  disk.  If  the 
book  be  carried  still  farther,  the  cross  will  again  come 
in  sight. 

There  is  no  doubt  but  that  the  portion  of  the  retina 
which  reacts  to  the  stimulus  of  light  is  the  layer  of  rods 
and  cones,  and  of  this  layer  the  cones  are  especially  sen- 
sitive. This  is  shown  by  the  fact  that  the  macula  lutea 
(yellow  spot)  is  the  portion  of  the  retina  which  is  the  most 
sensitive,  and  here  there  are  no  nerve-fibres,  but  rods  and 
cones,  and  in  the  fovea  centralis,  which  is  the  most  sen- 
sitive portion  of  the  macula,  only  cones  are  found.  How 
the  retina  converts  the  impressions  that  light-waves  pro- 
duce upon  it  into  nerve-impulses  is  still  an  unsettled 
question.     One  theory  is  that  the  light  produces  chem- 


NERVOUS  FUNCTIONS. 


321 


ical  changes  in  the  retina,  the  result  of  which  is  to  stim- 
ulate the  nerve-fibres;  another  theory  is  that  there  are 
thermic  influences  produced  by  the  light  which  have  the 
same  effect ;  while  a  third  theory  regards  the  pigment- 
cells  of  the  retina  as  in  some  way  connected  with  the 
phenomena. 

Movements  of  the  Eyeball. — The  eyeball  is  moved  by 
muscles  which  have  already,  to  some  extent,  been  consid- 
ered in  connection  with  the  functions  of  the  cranial  nerves. 
The  arrows  in  Fig.  74  indicate  the  direction  in  which  the 
different  muscles  act.     Thus  it  will  be  seen  that  the  in- 


*-4        4-<: 


Fig.  74. — Movements  of  the  Eyeballs:  i,  inferior  oblique;  2,  superior  rectus;  3,  ex- 
ternal rectus;  4,  internal  rectus;   5,  superior  oblique;  6,  inferior  rectus. 

ternal  rectus  rotates  the  eye  inward  ;  the  external  rectus, 
outward  ;  the  superior  rectus,  upward  and  inward  ;  the  in- 
ferior rectus,  downward  and  inward  ;  the  superior  oblique, 
downward  and  outward ;  the  inferior  oblique,  upward 
and  outward.  By  a  combination  of  two  of  these  muscles 
various  other  movements  are  produced;  thus  the  superior 
rectus  and  inferior  oblique,  acting  together,  rotate  the 
eyeball  vertically  upward,  while  the  inferior  rectus  and 
superior  oblique  jointly  rotate  it  vertically  downward. 
Appendages  of  the  Eye. — Lachrymal  Apparatus. — To 
21 


322 


HUMAN  PHYSIOLOGY. 


Fig.  75. — Muscles  of  the  Eye:  i,  the  palpebral  elevator;  2,  the  trochlear  muscle;  3, 
the  pulley  through  which  the  tendon  of  insertion  plays;  4,  superior  rectus  muscle; 
5,  inferior  rectus  muscle;  6,  external  rectus  muscle;  7,  8,  its  two  points  of  origin; 
9,  interval  through  which  pass  the  oculo-molor  and  abducens  nerves;  10,  inferior 
oblique  muscle ;  11,  optic  nerve  ;  12,  cut  surface  of  the  malar  process  of  the  superior 
maxillary  bone  ;  13,  the  nasal  notch  ;  A,  the  eyeball. 

keep  the  conjunctiva  (the  mucous  membrane  covering 
the  anterior  segment  of  the  sclerotic  and  the  cornea) 
moist  and  in  normal  condition  is  the  function  of  the 
tears.     They  are  secreted  by  the 
lachrymal    gland,    a    compound 
racemose  gland  lodged  in  a  de- 
pression at  the  upper  and  outer 
portion    of   the    orbit   (Fig.   'jG). 
Its  ducts,  about  seven  in  number, 
open  on  the  upper  and  outer  half 
of  the  conjunctiva  near  its  reflec- 
tion on  the  eyeball.    At  the  edge 
FxG.  76.-1, canaliculus;  2,  lach-  of  thc  uppcr  and  lowcr  cyclids, 
rymai  sac;  3,  nasal  duct;  4,   at    their    inucr    cxtrcmitics,    are 

plica  semilunaris ;    5,  caruncula  .  ,  ,       ,  1  •    \ 

lachryraaiis.  opcnmgs     (puncta     lachrymauaj 


NERVOUS  FUNCTIONS. 


323 


Fig.  77. — I,  lachrymal  gland;  2,  its  ducts; 

3,  punctum  lachrymale ;  a.  conjunctiva ; 

4,  Meibomian  glands. 


into  which  the  tears  pass  after  performing  their  func- 
tion. These  openings  are  the  beginnings  of  the  can- 
ahcuh,  which  open  into  the  lachrymal  sac,  or  the 
dilated  upper  extremity  of  the  nasal  duct,  which  dis- 
charges at  the  inferior 
meatus  of  the  nose,  the 
opening  here  being  partially 
closed  by  a  fold  of  mucous 
membrane,  the  valve  of 
Hasner. 

Meibomian  Glands.  —  On 
the  posterior  surface  of  the 
eyelids,  beneath  the  con- 
junctiva, are  the  Meibomian 
glands  (Fig.  yy),  thirty  in 
number  on  the  upper  and  fewer  on  the  lower  lid. 
Their  ducts  open  on  the  edges  of  the  lids,  and  their 
secretion  prevents  the  adhesion  of  the  lids  and  the 
tears  from  running  over  them  on  to  the  cheeks. 

5.  Sense  of  Hearing. — The  ear,  the  organ  of  hearing, 
is  divided  into  three  parts,  external,  middle,  and  internal, 
the  latter  being  essential,  while  the  others  are  accessory 
(Fig.  78). 

The  external  ear  consists  of  the  pinna  or  auricle  and 
the  external  auditory  canal  or  meatus.  The  office  of 
the  pinna  is  to  collect  the  sound-waves  and  direct  them 
to  the  canal,  which  they  traverse  to  reach  the  membrana 
tympani.  In  some  animals,  such  as  the  horse,  the  auri- 
cles are  very  important,  enabling  the  animal  to  detect 
the  direction  from  which  sounds  come,  and  they  are  cap- 
able of  considerable  movement;  but  in  man  they  are 
not  so  important,  although  when  the  hearing  is  defect- 
ive they  arc  of  assistance.     That  they  are  not  essential  to 


324 


HUMAN  PHYSIOLOGY. 


hearing  is  shown  by  the  fact  that  when  removed  hearing 
is  not  affected,  and  also  by  the  fact  that  in  birds,  where 
they  are  absent,  the  sense  of  hearing  is  well  marked. 


Fig.  78. — Semi-diagrammatic  Section  through  the  Right  Ear  (Czermak)  :  G,  external 
auditory  meatus;  T,  membrana  tympani  ;  P,  tympanic  cavity  :  o,  fenestra  ovalis ; 
r,  fenestra  rotunda  ;  B,  semicircular  canal ;  S,  cochlea  ;  Vt,  scala  vestibuli ;  Pt,  scala 
tympani. 

The  middle  ear,  tympanum,  or  tympanic  cavity,  is  sepa- 
rated from  the  meatus  by  the  membrana  tympani.     It  is  a 

cavity  in  the  petrous  portion 
of  the  temporal  bone,  is  filled 
with  air,  and  is  in  communi- 
cation with  the  pharynx  by 
means  of  the  Eustachian 
tube.  It  is  lined  with  mu- 
cous membrane  covered 
with  ciliated  epithelium. 
In  the  tympanic  cavity  are 
the     ossicles     (Fig.    79),    a 

Fig.  79.-Ossicles  of  the  Right  Ear.        chaiu     of   bonCS    which    COtt- 


lOeaiUeabr  process 


NERVOUS  FUNCTIONS. 


325 


nect  the  membrana  tympani  with  the  labyrinth  or  inter- 
nal ear.  These  bones  are  the  malleus,  the  incus,  and 
the  stapes,  otherwise  known  as  the  hammer,  the  anvil, 
and  the  stirrup,  so  called  from  their  resemblance  to  these 
objects. 

The  internal  car,  or  labyrintJi,  consists  of  three  parts, 
the  vestibule,  the  semicircular  canals,  and  the  cochlea. 


Fig.  80. — View  of  the  Interior  of  the  Left  Labyrinth  ;  the  bony  wall  of  the  labyrinth  is 
removed  superiorly  and  externally:  i,  fovea  semielliptica;  2,  fovea  hemispherica ; 
3,  common  opening  of  the  superior  and  posterior  semicircular  canals;  4,  opening  of 
the  aqueduct  of  the  vestibule;  5,  the  superior,  6,  the  posterior,  and  7,  the  external, 
semicircular  canals  ;  8,  spiral  tube  of  the  cochlea  (scala  tympani) ;  9,  opening  of  the 
aqueduct  of  the  cochlea ;  10,  placed  on  the  lamina  spiralis  in  the  scala  vestibuli 
(Sommering). 


CANALI*;     REUNIENS 

Fig.  81. — Diagram  of  the  Membranous  Labyrinth  (Gray). 

The.se  arc  cavities  in  the  temporal  bone  which  com- 
municate with  the  tympanum  through  the  fenestra  ovalis 
and    fenestra   rotunda,  and  with    the  internal   auditory 


326  HUMAN  PHYSIOLOGY. 

meatus,  through  which  runs  the  auditory  nerve,  the 
nerve  of  hearing.  These  cavities  form  the  osseous  laby- 
rinth. Within  these  is  the  membranous  labyrinth,  which 
contains  the  endolymph,  while  between  the  osseous  and 
membranous  labyrinths  is  a  fluid,  the  perilymph. 

Vestibule. — The  vestibule  is  a  common  cavity  with 
which  all  the  other  portions  of  the  labyrinth  are  in  com- 
munication. On  its  inner  wall  are  openings  through 
which  filaments  of  the  auditory  nerve  enter;  on  its  outer 
wall  is  the  fenestra  ovalis,  an  opening  closed  by  the  base 
of  the  stapes ;  posteriorly  the  semicircular  canals  com- 
municate by  five  openings,  and  anteriorly  is  the  opening 
of  communication  with  the  scala  vestibuli  of  the  cochlea. 
The  membranous  portion  of  the  vestibule  consists  of 
two  sacs,  the  utricle  and  the  saccule,  in  the  walls  of 
which  nerve-filaments  are  distributed,  and  within  are  the 
otoliths,  two  small  bodies  consisting  of  grains  of  car- 
bonate of  lime. 

Semicircular  Canals. — These  canals  are  three  in  num- 
ber. The  superior  semicircular  canal  is  vertical  and  at 
right  angles  to  the  posterior  surface  of  the  petrous  por- 
tion of  the  temporal  bone ;  the  posterior  is  also  vertical, 
but  is  parallel  with  the  surface  of  the  bone,  while  the 
external  or  horizontal  is  directed  outward  and  back- 
ward. The  arrangement  of  these  canals  is  such  that 
each  one  is  at  right  angles  with  the  other  two. 

Cochlea. — This  structure  resembles  somewhat  a  snail- 
shell  (Fig.  82).  In  its  central  portion  is  the  axis,  modi- 
olus, or  columella,  around  which  winds  a  spiral  canal 
divided  into  two  parts  by  a  partition  partly  bony  and 
partly  membranous.  The  bony  portion  is  the  lamina 
spiralis,  and  the  membranous  portion  is  the  membrana 
basilaris,  while  the   lower  canal  is  the  scala  tympani. 


NERVOUS  FUNCTIONS. 


327 


The  upper  canal  is  subdivided  by  the  membrane  of 
Reissner,  the  larger  part  of  the  canal  being  the  scala 
vestibuli,  and  the  smaller  the  scala  media,  also  called 
"  canal  of  the  cochlea."    In  the  latter  canal,  covered  over 


Fig.  82. — The  Bony  and  Membranous 
Cochlea  laid  open  :  st ,  scala  tympani ; 
sxi,  scala  vestibuli ;  cc,  scala  media  or 
ductus  cochlearis ;  h,  lamina  spiralis 
ossea ;  h,  helicotrema,  or  opening  con- 
necting the  scalse  tympani  and  vestib- 
uli. 


Fig.  83. — Section  through  one  of  the  Coils 
of  the  Cochlea  (diagrammatic) :  ST,  scala 
tympani ;  SV,  scala  vestibuli ;  CC,  canalis 
cochleae  or  canalis  membranaceus ;  R, 
membrane  of  Reissner;  A',?, lamina  spira- 
lis ossea  ;  Us,  limbus  lamina  spiralis  ;  ji', 
sulcus  spiralis;  nc,  cochlear  nerve;^i-,  gan- 
glion spirale;  /,  membrana  tectoria  (below 
the  membrana  tectoria  is  the  lamina  retic- 
ularis) ;  b,  membrana  basilaris  ;  Co,  rods 
ofCorti;  /jr/,  ligamentum  spirale  (Quain). 


by  the  membrana  tectoria,  is  the  organ  of  Corti,  which  is 
to  the  sense  of  hearing  what  the  retina  is  to  the  sense 
of  sight. 

Organ  of  Corti. — This  structure  is  located  on  the 
membrana  basilaris,  and  extends  throughout  the  length 
of  the  cochlea,  winding  with  it.  It  is  composed  of  cells 
whose  arrangement  has  been  likened  to  the  keyboard  of 
a  piano.  The  two  central  cells,  which  are  rod-like,  are 
the  inner  and  outer  rods  of  Corti.  They  form  an  angle 
with  each  other,  being  separated  at  the  base  and  meeting 
above,  leaving  a  space  between  them,  the  zona  arcuata. 
As  there  are  rows  of  these  rods,  this   space  forms  a 


328  HUMAN  PHYSIOLOGY. 

tunnel  extending  the  entire  length  of  the  cochlea.  The 
number  of  the  inner  rods  has  been  estimated  at  six 
thousand,  and  of  the  outer  at  four  thousand  five  hun- 
dred. At  the  sides  of  these  rods  are  rows  of  cells  which 
are  in  communication  with  the  terminal  filaments  of  the 
auditory  nerve.  On  the  tops  of  these  cells  are  hair- 
like processes,  or  cilia,  covered  by  a  delicate  membrane 
with  perforations,  through  which  pass  the  cilia  of  the 
outer  hair-cells.  The  membrana  tectoria  covers  all  these 
structures. 

Meclianisni  of  Hearing. — The  membrana  tympani  is 
made  to  vibrate  by  the  impulse  of  the  sound-waves 
which  reach  it;  through  the  ossicles  these  vibrations 
are  communicated  to  the  internal  ear,  the  base  of  the 
stapes  at  its  every  movement  sending  a  wave  through 
the  perilymph.  This  wave  passes  up  the  scala  vestibuli 
from  the  fenestra  ovalis,  which  the  base  of  the  stirrup 
closes,  to  the  top  of  the  cochlea,  and  comes  down  the 
scala  tympani  to  the  fenestra  rotunda,  in  its  course  pass- 
ing over  and  under  the  membranous  labyrinth  filled  with 
endolymph,  through  which  fluid  the  vibrations  are  com- 
municated to  the  terminal  filaments  of  the  auditory 
nerve.  It  is  supposed  that  these  waves  in  the  endo- 
lymph of  the  membranous  vestibule  cause  the  otoliths 
to  come  in  contact  with  the  nerve-filaments  and  to  stim- 
ulate them.  The  nerves  ending  in  the  semicircular 
canals  are  believed  to  preside  over  the  maintenance  of 
the  equilibrium  of  the  body,  and  not  to  be  connected  with 
hearing.  This  will  be  referred  to  later.  The  cochlear 
division  of  the  auditory  nerve  sends  into  the  modiolus 
of  the  cochlea  branches  that  pass  in  between  the  plates 
of  the  lamina  spiralis,  where  they  form  a  plexus  in  which 
are  ganglion-cells,  from  which  the  nerve-filaments  pass 


NERVOUS  FUNCTIONS.  329 

to  the  organ  of  Corti,  terminating,  it  is  believed,  in  the 
hair-cells. 

The  waves  already  referred  to  as  being  set  in  motion 
through  the  endolymph  pass  over  and  under  these  cells, 
with  which  the  nerve-filaments  are  connected,  and  cause 
the  basilar  membrane  on  which  they  rest  to  vibrate. 
This  motion  is  communicated  to  the  outer  rods  of  Corti, 
which  in  turn  pass  it  to  the  hairs  of  the  special  auditory 
cells  through  the  medium  of  the  perforated  membrane, 
and  from  there  it  passes  to  the  nerves.  Here  it  is  con- 
verted into  impulses  which  are  transmitted  to  the  brain, 
where  sound  is  produced. 

It  has  been  supposed  that  the  rods  of  Corti  are  so 
arranged  as  to  vibrate  with  particular  tones,  one  rod  for 
each  tone,  but  it  is  doubtful  whether  such  a  differentiation 
can  be  made  out  in  the  auditory  apparatus.  The  rods  are 
not  present  in  the  ears  of  birds,  and  there  is  no  reason 
to  believe  that  birds  cannot  appreciate  musical  tones. 
In  the  basilar  membrane  there  are  fibres  enough  to 
respond  to  all  the  notes  that  can  be  appreciated ;  that  is, 
from  thirty-three  waves  to  thirty-eight  thousand  waves 
in  a  second.  It  is  more  probable  that  the  rods  simply 
act  as  levers  to  communicate  the  vibrations  of  the  fibres 
of  the  basilar  membrane  to  the  terminal  nerve-filaments 
in  the  auditory  cells. 

Just  how  one  is  able  to  distingui.sh  the  differences  in 
the  intensity  (loudness),  pitch,  and  quality  of  sounds  is 
not  understood.  The  explanation  most  generally  ac- 
cepted at  the  present  time,  as  to  pitch  at  least,  is  that  as, 
when  a  tone  is  sung  over  the  strings  of  a  piano,  certain 
strings  are  set  in  vibration  sympathetically,  so  in  the 
basilar  membrane,  where,  as  in  the  piano,  there  are  fibres 
of  different  length,  these  respond  to  different  tones,  and 


330  HUMAN  PHYSIOLOGY. 

that  in  connection  with  each  tone  there  is  a  separate 
filament  of  the  auditory  nerve,  so  that  if  the  note  be  a 
high  one  a  certain  fibre  is  set  in  vibration,  and  the  nerve- 
filament  in  communication  with  it  transmits  an  impulse 
to  certain  cells  in  the  brain,  which  when  excited  give 
the  impression  of  a  high  tone,  and  so  with  other  tones 
and  other  nerve-cells. 

The  introduction  of  the  telephone  and  a  study  of  its 
mechanism  have  led  some  writers  to  question  the  expla- 
nations which  are  generally  accepted  of  the  mechanism 
of  hearing,  and  to  suggest  that  as  the  single  telephone 
wire  transmits  the  complex  sounds  produced  by  an 
orchestra  to  a  distance  where  they  are  reproduced  in  all 
their  variety  of  intensity,  pitch,  and  quality,  so  "  the 
cochlea  does  not  act  on  the  principle  of  sympathetic 
vibration,  but  that  the  hairs  of  all  its  auditory  cells 
vibrate  to  every  tone,  just  as  the  drum  of  the  ear  does ; 
that  there  is  no  analysis  of  complex  vibration  in  the 
cochlea  or  elsewhere  in  the  peripheral  mechanism  of  the 
ear ;  that  the  hair-cells  transform  sound-vibrations  into 
nerve-vibrations  similar  in  frequency  and  amplitude  to 
the  sound-vibrations ;  that  simple  and  complex  vibra- 
tions of  nerve-molecules  arrive  in  the  sensory  cells  of  the 
brain,  and  there  produce,  not  sound  again  of  course,  but 
the  sensations  of  sound,  the  nature  of  which  depends  not 
upon  the  stimulation  of  different  sensory  cells,  but  on  the 
frequency,  the  amplitude,  and  the  form  of  the  vibrations 
coming  into  the  cells,  probably  through  all  the  fibres  of 
the  auditory  nerve."  This  explanation  has  been  put 
forth  by  Prof.  William  Rutherford  under  the  title  of  the 
"  Telephone  Theory  of  the  Sense  of  Hearing." 

Although  sound-waves  for  the  most  part  are  trans- 
mitted to  the  internal  ear  through  the  tympanum,  they 


NERVOUS  FUNCTIONS.  331 

may  also  be  transmitted  through  the  bones  of  the  head. 
Thus  vibrating  bodies— a  tuning-fork,  for  example— may 
be  placed  on  the  top  of  the  head  and  the  sound  will  be 
heard,  or  it  may  be  held  between  the  teeth  with  the  same 
result.  This  fact  is  made  use  of  in  the  audiphone,  a  fan- 
like device  held  in  the  teeth  by  the  deaf  If  the  essential 
portions  of  the  auditory  apparatus  be  so  diseased  as  to 
cause  deafness,  no  such  device  as  the  audiphone  will  be 
of  any  use. 

Eustachian  Tube.— To  permit  the  membrana  tympani 
to  respond  properly  to  the  sound-waves  that  reach  it,  the 
pressure  of  the  atmosphere  must  be  the  same  on  both 
sides,  and  as  the  external  pressure  is  subject  to  constant 
changes,  a  provision  for  a  similar  change  on  the  tym- 
panic side  is  essential.  This  is  accomplished  by  the 
Eustachian  tube,  the  channel  of  connection  between  the 
tympanic  cavity  and  the  pharynx.  The  pharyngeal 
orifice  of  this  tube  is  closed  except  during  sv/allowing, 
at  which  time  it  is  opened.  If  it  were  always  open  the 
sound  of  one's  own  voice  would  be  so  loud  as  to  be  ex- 
tremely disagreeable. 

Semicircular  Canals. — These  structures  have  probably 
no  connection  with  hearing,  nor  are  they  designed  to 
distinguish  the  direction  from  which  sound-waves  come, 
as  when  diseased  the  hearing  is  in  no  wise  affected,  but 
under  these  circumstances  there  is  a  feeling  of  giddiness 
and  the  movements  of  the  body  are  uncertain.  If  one 
of  them  be  cut,  the  head  of  the  animal  experimented 
upon  is  violently  moved  to  and  fro  in  the  plane  of  the 
canal  which  was  divided,  and  it  walks  in  an  unsteady 
manner.  The  canals  are  therefore  regarded  as  being 
connected  with  the  maintenance  of  equilibrium. 

Sympathetic  Nervous  System. — The  sympathetic  ner- 


332 


HUMAN  PHYSIOLOGY. 


Fig.  84. — Diagrammatic  view  of  the 
Sympathetic  Cord  of  the  Right  Side, 
showing  its  connections  with  the  prin- 
cipal cerebro-spinal  nerves  and  the 
main  prseaortic  plexuses.  (Reduced 
from  Quain's  Anatomy.) 

Cerebro-spinal  Nerves. — VI.,  a  por- 
tion of  the  sixth  cranial  as  it  passes 
through  the  cavernous  sinus,  receiving 
two  twigs  from  the  carotid  plexus  of 
the  sympathetic  nerve  ;  O,  ophthalmic 
ganglion  connected  by  a  twig  with  the 
carotid  plexus;  M,  connection  of  the 
spheno-palatine  ganglion  by  the  Vidian 
nerve  with  the  carotid  plexus  ;  C,  cervi- 
cal plexus  ;  Br,  brachial  plexus ;  D  6, 
sixth  intercostal  nerve ;  D  12,  twelfth  ; 
L  3,  third  lumbar  nerve;  S  i,  first  sac- 
ral nerve ;  S  3,  third ;  S  s,  fifth  ;  Cr, 
anterior  crural  nerve  ;  Cr,  great  sciatic  ; 
p7i,  vagus  in  the  lower  part  of  the  neck ; 
r,  recurrent  nerve  winding  round  the 
subclavian  artery. 

Sympathetic  Cord. — c,  superior  cer- 
vical ganglion  ;  c' ,  second,  or  middle  ; 
c" ,  inferior  ;  from  each  of  these  ganglia 
cardiac  nerves  (all  deep  on  this  side) 
are  seen  descending  to  the  cardiac 
plexus  ;  d  i,  placed  immediately  below 
the  first  dorsal  sympathetic  ganglion  ; 
I  d  6,  \%  opposite  the  sixth ;  /  1,  first 
lumbar  ganglion  ;  c  g,  the  terminal  or 
coccygeal  ganglion. 

Prceaortic  and  Visceral  Plexuses. — 
//,  pharyngeal,  and,  lower  down,  lar- 
yngeal plexus ;  pi,  post,  pulmonary 
plexus  spreading  from  the  vagus  on  the 
back  of  the  right  bronchus  ;  ca,  on  the 
aorta,  the  cardiac  plexus,  toward  which, 
in  addition  to  the  cardiac  nerve  from 
the  three  cervical  sympathetic  ganglia, 
other  branches  are  seen  descending 
from  the  vagus  and  recurrent  nerves  ; 
CO,  right  or  posterior  and  co' ,  left  or 
anterior  coronary  plexus  ;  o,  oesophageal  plexus  in  long  meshes  on  the  gullet ;  sp,  great 
splanchnic  nerve  formed  by  branches  from  the  fifth,  sixth,  seventh,  eighth,  and  ninth 
dorsal  ganglia;  +,  small  splanchnic  from  the  ninth  and  tenth:  +  -\-,  smallest  or  third 
splanchnic  from  the  eleventh  ;  the  first  and  second  of  these  are  shown  joining  the  solar 
plexus,  so:  the  third  descending  to  the  renal  plexus,  re :  connecting  branches  between 
the  solar  plexus  and  the  vagi  are  also  represented  ;  pn' ,  above  the  place  where  the  right 
vagus  passes  to  the  lower  or  posterior  surface  of  the  stomach ;  pn" ,  the  left  distributed 
on  the  anterior  or  upper  surface  of  the  cardiac  portion  of  the  organ :  from  the  solar 


NERVOUS  FUNCTIONS. 


333 


vous  system  consists  of  ganglia  and  nerves  (Fig.  84).  The 
four  ganglia  which  some  writers  describe  as  sympathetic 
ganglia  of  the  head,  have  been  described  in  connection 
with  the  trigeminus. 

Sympathetic  Ganglia  and  Nerves. — From  the  base  of 
the  skull  to  the  end  of  the  spinal  column  there  is  on 
each  side  of  the  latter  a  chain  of  ganglia  (twenty-four 
in  number)  which  are  connected  in  a  series  by  nervous 
matter,  each  being  spoken  of  as  a  ganglionic  cord.  At 
the  coccyx  these  cords  unite  in  one  ganglion,  the  gan- 
glion impar,  and  they  are  called  "  lateral,"  "  vertebral,"  or 
"  vaso-motor  "  ganglia.  Besides  these  ganglia  there  are 
three  gangliated  plexuses — the  cardiac  in  the  thoracic 
cavity,  the  solar  in  the  a"bdominal,  and  the  hypogastric  in 
the  pelvic  cavity.  These  are  spoken  of  as  "  collateral  " 
ganglia.  There  are  besides  ganglia  in  the  viscera,  as, 
for  instance,  in  the  heart;  these  are  terminal  ganglia. 
The  ganglia  on  the  posterior  roots  of  spinal  nerves  are 
also  regarded  as  belonging  to  the  sympathetic  system. 

The  sympathetic  ganglia  differ  in  no  important  par- 
ticular from  the  ganglia  already  described.  The  nerve- 
cells  are  small,  and  are  to  a  considerable  extent  unipolar. 
The  nervous  matter  which  connects  the  ganglia  consists 
of  both  white  and  gray  nerve-fibres.      The  ganglia  are 

plexus  large  branches  are  seen  surrounding  the  arteries  of  the  cosliac  axis,  and  descend- 
ing to  }ns,  the  sup.  mesenteric  plexus :  opposite  to  this  is  an  indication  of  the  supra- 
renal plexus;  below  re  (the  renal  plexus),  the  spermatic  plexus  is  also  indicated;  ao, 
on  the  front  of  the  aorta,  marks  the  aortic  plexus,  formed  by  nerves  descending  from 
the  solar  and  sup.  mesenteric  plexuses  and  from  the  lumbar  ganglia;  ml,  the  inf. 
mesenteric  plexus  surrounding  the  corresponding  artery ;  hy,  hypogastric  plexus 
placed  between  the  common  iliac  vessels,  connected  above  with  the  aortic  plexus, 
receiving  nerves  from  the  lower  lumbar  ganglia,  and  dividing  below  into  the  right  and 
left  pelvic  or  inf.  hypogastric  plexuses  ;  //,  the  right  pelvic  plexus  ;  from  this  the  nerves 
descending  are  joined  by  those  from  the  plexus  on  the  sup.  hemorrhoidal  vessels,  mi' ,  by 
ner\'es  from  the  sacral  ganglia,  and  by  visceral  nerves  from  the  third  and  fourth  sacral 
spinal  nerves,  and  there  are  thus  formed  the  rectal,  vesical,  and  other  plexuses,  which 
ramify  upon  the  viscera,  as  toward  ir,  and  v,  the  rectum  and  bladder. 


334  HUMAN  PHYSIOLOGY. 

also  intimately  connected  with  the  cerebro-spinal  nerves 
by  both  white  and  gray  fibres.  The  white  fibres  which 
pass  fi-om  the  spinal  nerves  to  the  ganglia  are  con- 
tinuous with  the  white  fibres  just  described  in  the 
branches  of  communication  between  the  ganglia.  The 
gray  fibres  pass  fi-om  the  ganglia  to  the  spinal  nerves. 

The  most  recent  writers  are  inclined  to  regard  the 
cerebro-spinal  and  sympathetic  systems  not  as  distinct, 
but  as  parts  of  one  great  whole,  and  the  intimate  rela- 
tionship between  the  two  is  strongly  confirmatory  of  this 
view.  The  history  of  the  development  of  both  is  the 
same  :  the  vaso-motor  nerves,  which  are  called  "  sympa- 
thetic," have  their  real  origin  in  the  cord  and  medulla, 
and,  so  far  as  known,  the  ganglia  of  the  sympathetic  do 
not  respond  reflexly  to  stimuli,  as  they  would  be  expected 
to  do  if  they  were  independent  centres. 

Functions  of  the  Sympathetic. — The  efferent  fibres  of 
the  sympathetic  are  distributed  to  the  muscles  of  the 
vascular  system  as  vaso-motor  fibres ;  that  is,  vaso-con- 
strictor  and  cardio-accelerator,  and  vaso-dilator  and  car- 
dio-inhibitory.  The  vaso-constrictor  and  cardio-inhib- 
itory  nerves  pass  out  from  the  spinal  cord  by  the  anterior 
roots  of  the  spinal  nerves  from  the  second  dorsal  to  the 
second  lumbar,  and  pass  to  the  lateral  ganglia  of  the 
sympathetic.  They  are  at  this  time  medullated  fibres, 
but  in  the  ganglia  they  become  non-medullated,  and  also 
increase  in  number,  and  go  to  their  various  points  of 
distribution.  The  cardio-accelerator  fibres  pass  into  the 
stellate  inferior  cervical  ganglion,  where  they  lose  their 
medullary  sheath,  and  leave  it  as  non-medullated  fibres, 
to  be  distributed  to  the  heart.  The  vaso-dilator  or  vaso- 
inhibitory  nerves  are  doubtless  as  numerous  as  the  vaso- 
constrictor, but  far  less  is  known  of  them.     The  nervi 


NERVOUS  FUNCTIONS.  335 

erigentes  which  pass  to  the  hypogastric  plexus,  the 
chorda  tympani,  and  the  small  petrosal  nerve  are  illus- 
trations of  this  class  of  inhibitory  fibres,  as  is  also  the 
cardio-vagus,  the  inhibitory  nerve  of  the  heart.  These 
nerve-fibres  have  no  connection  with  the  lateral  ganglia, 
but  they  pass  on  to  the  collateral  or  terminal  ganglia. 

The  sympathetic  efferent  fibres  are  also  distributed  to 
the  muscles  of  the  viscera,  and  are  viscero-motor  and 
viscero-inhibitory.  The  fibres  which  supply  innervation 
to  the  muscles  of  the  lower  portion  of  the  oesophagus, 
the  stomach,  and  the  intestines,  by  virtue  of  which  they 
perform  their  peristaltic  movements,  are  of  this  character. 
The  viscero-inhibitory  are  but  little  understood.  In  addi- 
tion to  these  there  are  also  glandular  nerves  which  are 
distributed  to  secreting  organs :  of  these  little  is  known 
except  as  to  the  parotid,  submaxillary,  and  lachrymal 
glands. 

The  functions  of  the  sympathetic  ganglia  are,  so  far 
as  known,  threefold  :  i,  to  change  the  medullated  into 
non-medullated  fibres ;  2,  to  divide  the  fibres  into  a 
large  number  of  filaments ;  and  3,  to  exercise  a  trophic 
or  nutritive  influence  on  the  distal  portions  of  the  nerves, 
and  possibly  on  the  structures  to  which  they  are  distrib- 
uted. The  centres  in  the  cord  with  which  the  sympa- 
thetic nerves  are  connected  are  Clark's  vesicular  column, 
Stilling's  sacral  nucleus,  which  is  in  that  part  of  the  cord 
corresponding  to  the  second  and  third  segments  of  the 
sacrum,  and  a  third  in  the  neighborhood  of  the  vagal 
nucleus,  that  is,  the  portion  of  the  medulla  in  which  the 
vagus  nerve  has  its  origin. 


IV.  REPRODUCTIVE   FUNCTIONS. 

The  reproductive  functions  are  those  concerned  in  the 
perpetuation  of  the  species.  In  the  lower  forms  of  ani- 
mal life,  where  the  individual  consists  of  a  single  cell, 
this  process  of  reproduction  is  very  simple,  consisting 
of  the  division  of  the  cell  into  two,  each  of  which  has 
the  same  power  of  dividing  to  form  new  individuals  in 
the  same  manner  as  itself  was  formed.  This  is  asexual 
reproduction.  In  the  higher  animals  the  reproduction  is 
sexual ;  that  is,  it  requires  the  union  of  two  elements  pro- 
duced in  the  organs  of  two  individuals,  the  male  and  the 
female,  neither  of  which  can  accomplish  the  process  alone. 

I.  Reproductive  Organs. 

These  organs,  which  are  also  called  the  genital  or 
generative  organs,  are  in  the  male  the  testes,  each  with 
its  duct,  the  vas  deferens,  and  the  reservoir,  the  vesicula 
seminalis,  and  the  penis  ;  and  in  the  female,  the  ovaries, 
Fallopian  tubes,  uterus,  and  vagina. 

Genital  Organs  of  the  Male. —  Testes. — The  testes,  or 
testicles  (Fig.  85),  two  in  number,  are  situated  in  the 
scrotum.  They  are  composed  of  lobules,  the  number 
of  which  in  each  testis  is  variously  estimated  at  from 
two  hundred  and  fifty  to  four  hundred.  In  each  lobule 
are  convoluted  seminiferous  tubules,  tubuli  seminiferi, 
varying  in  number  from  one  to  three. 

Spermatozoa. — In  the  interior  of  the  testes  are  several 
layers  of  epithelial  cells  which,  from  the  fact  that  they 
form  the  essential  part  of  the  semen,  are  called  "  sem- 
inal cells."  At  the  time  of  puberty  some  of  these  cells, 
mother-cells,    undergo    division,    producing    thereby   a 

336 


REPRODUCIIVE  FUNCTIONS. 


337 


Fig.  85.— Testicle  and  Epididymis  of  the  Human  Subject:  a,  testicle  ;  b,  lobules  of  the 
testicle  ;  c,  vasa  recta  ;  d,  rete  testis ;  c,  vasa  efferentia  ;  f,  cones  of  the  globus 
major  of  the  epididymis ;  g,  epididymis  ;  h,  vas  deferens ;  i,  vas  aberrans ;  in, 
branches  of  the  spermatic  artery  to  the  testicle  and  epididymis;  n,  ramification  of 
the  artery  upon  the  testicle  and  epididymis  ;  o,  deferential  artery ;  /,  anastomosis 
of  the  deferential  with  the  spermatic  artery  (KiiUiker). 


Fk;.  86.— Section  ol  the  'I'ubull  bcminiferi  of  a  Rat  (Schafer) :  a,  tubuli  in  which  the 
spermatozoa  are  not  fully  developed;  i^,  spermatozoa  more  developed;  f,  spermatozoa 
still  more  developed. 
22 


338 


HUMAN  PHYSIOLOGY. 


number  of  smaller  cells.  These  daughter-cells  are 
called  "  spermatoblasts,"  and  it  is  these  cells  that  are 
changed  into  the  spermatozoa  which  are  the  fecundat- 
ing elements  of  the  semen.  Each  spermatozoon  con- 
sists of  a  head,  a  body,  and 
a  tail.  These  terms  do  not 
indicate  any  special  organ- 
ization, but  are  used  simply 
for  purposes  of  description, 
as  we  speak  of  the  head  of 
an  arrow.  The  spermatozoa 
of  different  animals  vary  in 
size,  although  their  general 
appearance  is  much  the 
same.  The  human  sperma- 
tozoon is  about  0.055  mm. 
long  (Fig.  87,  a),  while  that 
of  menobranchus  is  0.57  mm. 
(Fig.  ^j ,  c).  These  structures 
are  endowed  with  the  power 
of  locomotion,  due  to  the 
vibratory  motion  of  their 
Fig.  87,-Spermatozoa :  a,  human ;  /,.  of  ^^ils  or  fiagclla,  by  which 
,  of  menobranchus  (magnified  they  Can  travcl  for  a  Consid- 
erable distance  in  the  gen- 
erative passages  of  the  female. 

The  seminiferous  tubules  terminate  at  the  apices  of 
the  lobules  in  the  vasa  recta  (straight  tubes),  about  thirty 
in  number.  In  the  mediastinum  these  tubes  form  a  net- 
work, the  rete  testis,  the  vessels  of  which  end  in  the 
vasa  efferentia,  about  fifteen  in  number.  These  vessels 
connect  the  testicles  with  the  epididymis,  the  continua- 
tion of  which  is  the  vas  deferens. 


the  rat ; 
480  times). 


REPRODUCTIVE   FUNCTIONS. 


339 


Vas  Deferens  and  Vesienla  Seniina/is. — The  vas  deferens 
may  be  regarded  as  the  excretory  duct  of  the  testis  (Fig. 
88).  It  terminates  at  the  base 
of  the  bladder,  where  it  unites 
with  the  duct  of  the  vesicula 
seminahs  to  form  the  ejaculatory 
duct,  which  discharges  into  the 
prostatic  portion  of  the  urethra. 

The  spermatozoa  traverse  the 
following  vessels  after  leaving 
the  seminiferous  tubules :  vasa 
recta,  rete  testis,  epididymis,  and 
vas  deferens.  The  mucous  mem- 
brane lining  each  of  these  chan- 
nels adds  its  secretion  as  the 
spermatozoa  pass  along,  until 
the  vesicula  seminalis  is  reached, 
which  acts  as  a  reservoir  for  the 
semen.  The  lining  of  the  vasa 
recta  and  the  rete  testis  is  a 
single  layer  of  flattened  epi- 
thelium ;  that  of  the  vasa  effer- 
entia,  the  epididymis,  and  the  vas  deferens  is  columnar 
and  ciliated.  The  spermatozoa,  up  to  the  time  that 
they  reach  the  seminal  vesicles,  display  but  little  of  their 
characteri-stic  motion.  This  is  probably  due  to  the  fact 
that  they  are  more  or  less  agglutinated,  but  in  these 
reservoirs  there  is  formed  a  considerable  quantity  of 
secretion  which  dilutes  the  semen,  and  at  this  time  the 
oscillatory  motions  of  the  spermatozoa  become  very 
marked. 

Genital  Organs  of  the  Female. — Ovary. — The  ovaries 
(I''igs.  89,  90,  91J,  two  in  number,  are  analogues  of  the 


IG.  88. — Posterior  View  of  the 
Fundus  of  the  Bladder  :  i,  peri- 
toneum extending  as  far  down 
as  the  transverse  line  ;  2,  ureters  ; 
3,  deferent  canals;  4,  seminal 
vesicle  of  the  left  side  ;  5,  right 
seminal  vesicle  dissected  so  as 
to  show  its  tubular  character  ; 
6,  dnct  of  the  seminal  vesicle, 
joining  the  deferent  canal  to 
form,  7,  the  ejaculatory  duct ;  8, 
prostate;  9,  membranous  por- 
tion of  the  urethra. 


340 


HUMAN  PHYSIOLOGY. 


testicles.  They  are  situated  in  the  posterior  part  of  the 
broad  Hgament,  one  on  each  side  of  the  uterus.  The 
human  ovar}-  weighs  about  8  grammes,  and  consists  of 
stroma  and  Graafian  vesicles  or  follicles.  The  stroma  is 
made  up  of  spindle-shaped  cells,  which  are  regarded  by 
some  authorities  as  non-striated  muscle-cells,  and  by 
others  as  connective-tissue  cells,  together  with  connective 
tissue.     The   outer  layer  of  the  ovary,  formerly  called 


Fig.  89. — Section  of  the  Ovary  of  a  Cat,  enlarged  six  times  (Schron)  :  i,  outer  covering 
and  free  border  of  the  ovary  (epithelium  and  albuginea)  ;  i',  attached  border  ;  2,  vas- 
cular zone,  or  medullary  substance ;  3,  parenchymatous  zone,  or  cortical  substance ; 
4,  blood-vessels  ;  5,  Graafian  follicles  in  their  earliest  stages,  lying  near  the  surface; 
6,  7,  S,  more  advanced  follicles,  imbedded  more  deeply  in  the  stroma ;  9,  an  almost 
mature  follicle,  containing  the  ovTim  in  its  deepest  part ;  9',  a  follicle  from  which  the 
ovum  has  accidentally  escaped;  10,  corpns  luteum. 


"tunica  albuginea,"  is  now  regarded  as  condensed  stroma. 
The  covering  of  the  ovary  is  a  single  layer  of  columnar 
cells,  the  germinal  epithelium  of  Waldeyer.  This  is 
quite  different  in  appearance  and  structure  from  the 
peritoneum,  which  is  covered  hy  flattened  endothelium. 
The  Graafian  vesicles  are  sacs  in  the  ovarian  stroma 
var}'ing  in  size  according  to  the  period  of  their  develop- 
ment.    The  wall  of  a  vesicle  is  called  the  "  membrana 


REPRODUCTIVE  FUNCTIONS. 


341 


propria,"  and  is  made  up  of  two  layers — an  external 
layer  of  capillary  blood-vessels,  the  tunica  vasculosa, 
and  an  internal  or  fibrous  layer,  the  tunica  fibrosa.  The 
latter  is  lined  with  granular  cells  arranged  somewhat  in 
the  form  of  a  membrane,  making  the  membrana  or  tunica 
granulosa.  At  one  part  of  this  membrane  the  cells  are 
accumulated,  forming  the  discus  or  cumulus  proligerus, 


Fig.  90. — Part  of  the  same  section  as  represented  in  Fig.  89,  more  highly  enlarged 
(Schron) :  i,  small  Graafian  follicles  near  the  surface  ;  2,  fibrous  stroma  ;  3,  3',  less 
fibrous,  more  superficial  stroma  ;  4,  blood-vessels  ;  5,  a  follicle  still  further  advanced  ; 
6,  one  or  two  more  deeply  placed  ;  7,  one  further  developed,  enclosed  by  a  prolonga- 
tion of  the  fibrous  stroma;  8,  part  of  the  largest  follicle;  a,  membrana  granulosa; 
b,  discus  proligerus  ;  c,  ovum  ;  </,  germinal  vesicle  ;  e,  germinal  spot. 


in  the  midst  of  which  an  ovum  is  imbedded.  Between 
the  discus  proligerus  and  the  membrana  granulosa,  ex- 
cept where  the  two  are  united,  is  a  fluid,  the  liquor 
folliculi. 

When  during  foetal  life  the  ovary  is  formed,  some  of 
these  cells,  which  have  been  mentioned  above  as  com- 


342 


HUMAN  PHYSIOL  OGY. 


posing  the  germinal  epithelium  of  Waldeyer,  come  to 
be  situated  in  the  stroma,  and  by  a  growth  of  the  latter 
they  are  cut  off  from  the  surface.  Around  them  the 
ovicapsule  forms,  and  the  included  cells,  with  one  ex- 
ception, become  the  cells  of  the  membrana  granulosa. 
The  one  cell  referred  to  becomes  the  oviivi. 

Parovarium. — The  parovarium  (Fig.  91),  also  called  the 
"organ  of  Rosenmiiller,"  is  above  the  ovary  in  the  broad 


Fig.  91. — Posterior  View  of  Left  Uterine  Appendages  (Henle) :  i,  uterus  ;  2,  Fallopian 
tubes  ;  3,  fimbriated  extremity  and  opening  of  the  Fallopian  tube  ;  4,  parovarium  ; 
5,  ovary  ;  6,  broad  ligament  ;  7,  ovarian  ligament;  8,  infundibulo-pelvic  ligament. 


ligament,  between  the  latter  and  the  Fallopian  tube.     It 
is  the  remains  of  the  Wolffian  body,  a  foetal  organ. 

Ovum. — The  human  ovum,  which  is  on  an  average 
0.25  mm.  in  diameter,  is  composed  of  an  external  envel- 
oping membrane,  the  vitelline  membrane  or  zona  pellu- 
cida,  within  which  is  an  albuminous  material,  the  vitellus, 
in  the  midst  of  which  is  the  germinal  vesicle  with  its 
contained  germinal  spot. 


REPRODUCTIVE   FUNCTIONS. 


343 


Fig.  92.— Mature  Ovum  of  Rabbit  (Waldeyer) :  a,  cells  from  the  discus  proligenis 
(epithelium  of  ovum) ;  i^,  zona  pellucida  ;  c,  vitellus  ;  </,  germinal  vesicle  ;  f,  germinal 
spot;y,  large  globules  with  dull  lustre  in  the  germinal  vesicle. 


Fallopian  Tubes. — The  Fallopian  tubes  are  each  about 
10  cm.  long,  and  extend  from  the  angles  of  the  uterus  to 


Fir;.  <33.— Fallopian  TuVje  laid  open  (from  Playfair,  source  unknown) :  a,  /',  uterine 
portion  of  tube;  c,ti,(u\<U  of  mucou-  membrane;  r,  tubo-ovarian  ligament,  or 
fimbria  ovarica  ;  /,  ovary  ;  g,  round  ligament. 


344 


HUMAN  PHYSIOLOGY. 


the  sides  of  the  pelvis.  Each  tube  is  composed  of  three 
coats — serous,  muscular,  and  mucous.  The  muscular 
coat  contains  both  longitudinal  and  circular  fibres.  The 
mucous  coat  is  covered  by  columnar  ciliated  epithe- 
lium, and  it  consists  of  three  parts,  the  isthmus,  the 
ampulla,  and  the  infundibulum.     In  this  latter  portion 


Fig.  94, — Vertical  Section  through  the  Mucous  Membrane  of  the  Human  Uterus 
(Turner):  <?,  columnar  epithelium — the  cilia  are  not  represented;  g,g,  utricular 
glands  ;  ct,  interglandular  connective  tissue  ;  v,  v,  blood-vessels  :  jnm,  muscular  layer. 


is  the  ostium  abdominale,  the  outer  opening  of  the 
tube,  which  is  surrounded  by  the  fimbriae,  one  of  which, 
the  fimbria  ovarica,  is  attached  to  the  ovary.  The  fim- 
briae are  also  lined  by  ciliated  epithelium.     The  canal 


REPRODUCTIVE   FUNCTIONS. 


345 


of  the  tube  is,  at  its  junction  with  the  uterus,  very  nar 
row,    scarcely    admitting    a 
bristle  ;  in  the  other  portion 
it  is  larger. 

Uterus. — The  uterus  is 
about  7.5  cm.  long,  5  cm. 
broad,  and  2.5  cm.  thick,  and 
weighs  about  32  grammes. 
It  is  divided  into  body  and 
neck — corpus  and  cervix — 
and  consists  of  three  coats 
— serous,  muscular,  and  mu- 
cous. The  mucous  coat  is 
covered  by  columnar  cili- 
ated epithelium,  except  at 
the  lower  third  of  the  cer- 
vix, where  the  cilia  are  ab- 
sent, and  the  epithelium 
gradually  changes  until  at 
the  external  os  it  is  squamous.  In  the  mucous  mem- 
brane of  the  body  are  the  uterine  glands. 


A^^^i'^fsM^^i^ 


3 

Fig.  95. — Section  of  the  Mucous  Mem- 
brane of  the  Uterus,  parallel  to  the 
surface  (Henle)  :  i,  2,  3,  glands  (the 
epithelium  has  fallen  out  from  2) ;  4, 
blood-vessel. 


2.  Ovulation. 

At  undetermined  periods  the  liquor  folliculi  of  the 
Graafian  vesicles  increases,  and  as  a  result  the  membrana 
propria  becomes  distended  until  the  distention  reaches 
such  a  degree  that  this  membrane  bursts  and  the  contents, 
including  the  ovum,  are  discharged.  The  ripening  and 
discharge  of  ova  constitute  ovulation,  which  is  believed  by 
many  authorities  to  occur  at  regular  intervals  of  about 
four  weeks.  Others  think  tliat  this  process  does  not  take 
place  so  frequently,  and  that  the  intervals  are  very  irreg- 


346  HUMAN  PHYSIOLOGY. 

ular  and  unknown.  J.  Bland  Sutton,  in  his  Surgical 
Diseases  of  the  Ovaries  and  Fallopian  Tubes,  says :  "In 
the  ovary  of  the  human  foetus  ova  ripen,  form  folHcles, 
and  undergo  suppression  during  the  last  month  of  intra- 
uterine life.  The  life  of  the  human  ovary  may  be  divided 
into  the  following  periods  of  activity  and  repose :  The 
first  period  extends  from  the  seventh  month  of  intra- 
uterine life  to  the  end  of  the  first  year.  Ova  ripen  in 
such  abundance  that  in  some  cases  a  marked  diminution 
in  the  number  of  the  ova  is  appreciable  at  the  second 
year  after  birth.  To  this  succeeds  a  period  of  compar- 
ative repose,  terminating  at  the  tenth  or  twelfth  year; 
then  the  ripening  of  ova  is  again  easily  detected,  and 
goes  on  independently  of  menstruation,  even  after  the 
accession  of  the  climacteric." 

In  an  uncertain  proportion  of  instances  the  ova  find 
their  way  into  the  Fallopian  tube.  The  mechanism  by 
which  this  is  accomplished  is  still  a  matter  of  doubt. 
One  theory  maintains  that  the  fimbriated  extremity  is 
so  approximated  to  the  ovary  as  to  bring  the  ostium 
abdominale  against  the  part  at  which  the  Graafian  vesi- 
cle is  about  to  rupture,  and  that  the  escaping  ovum  thus 
enters  the  tube.  Tait  has  found  in  certain  cases  upon 
which  he  has  operated  the  tube  grasping  the  ovary,  and 
he  attributes  this  action  to  muscular  fibres  which  develop 
at  the  period  of  puberty  and  which  atrophy  at  the  men- 
opause, so  that  ova  can  enter  the  tube  only  during  the 
active  life  of  these  fibres,  and  then,  and  then  only,  can 
pregnancy  take  place,  though  both  before  puberty  and 
after  the  menopause  ovulation  may  occur,  the  ova  under 
these  circumstances  falling  into  the  abdominal  cavity, 
where  they  disintegrate.  According  to  this  theory,  if 
ovulation  takes  place  and  the  tube  does  not  grasp  the 


REPRODUCTIVE  FUNCTIONS.  347 

ovary,  the  ovum  when  discharged  would  not  enter  the 
tube,  but  would  fall  into  the  abdominal  cavity. 

The  second  theory  is,  that  this  grasping  of  the  ovary 
by  the  tube  does  not  occur,  but  that  the  ovum  is  carried 
into  the  ostium  abdominale  by  the  current  created  by 
the  ciliated  epithelium  lining  the  tube  and  the  fimbriae. 
The  fimbria  ovarica,  which  is  attached  to  the  ovary, 
forms  a  little  groove  leading  to  the  ostium,  and  if  an 
ovum  should  find  its  way  into  it  the  ciliated  epithelium 
would  doubtless  carry  it  to  the  opening  of  the  tube. 

While  neither  of  these  theories  has  been  demon- 
strated as  the  sole  explanation  of  the  cause  of  the  pass- 
age of  the  ovum  into  the  tube,  it  is  possible  that  both 
are  in  a  measure  correct.  If  the  actual  grasping  of  the 
ovary  by  the  tube  does  not,  as  a  rule,  occur,  there  may 
still  be  a  partial  approximation  and  the  current  may 
complete  the  process.  It  is  to  be  remembered  that  the 
ovum  is  but  0.25  mm.  in  diameter,  and  there  seems  no 
reason  to  question  the  power  of  the  current  to  draw  so 
small  a  body  into  the  tube.  Once  in  the  tube,  it  is  car- 
ried on  to  the  uterus  by  the  ciliated  epithelium. 

3.   Menstruation. 

At  about  the  age  of  fourteen  years  a  bloody  discharge 
takes  place  from  the  vagina  at  intervals  of  about  four 
weeks.  This  is  the  menses,  and  the  process  is  nioistrii- 
atio7i.  It  should  be  noted  that  the  period  of  life  at 
which  menstruation  appears  is  by  no  means  uniform  in 
all  individuals. 

Prof.  Skene  lays  down  the  following  rules  in  his  Dis- 
eases of  Woine7i : 

I.  Menstruation    should  begin   at  puberty;    that   is, 


348  HUMAN  PHYSIOLOGY. 

when  the  woman  is  maturely  developed,  no  matter  what 
the  age  may  be. 

2.  It  should  recur  at  regular  intervals ;  about  every 
twenty-eight  days  is  the  average  time.  A  regular  peri- 
odicity is  normal,  but  the  duration  of  the  periods  often 
differs  in  different  persons. 

3.  The  discharge  should  always  be  fluid  in  consistence 
and  sanguineous  in  color. 

4.  The  flow  should  continue  a  definite  length  of  time, 
the  duration  depending  upon  the  habit  of  each  case ;  at 
least  there  should  not  be  any  great  deviation  from  this 
rule.  The  duration  is  usually  from  three  to  five  days, 
and  the  total  amount  is  about  four  or  five  ounces. 

At  about  the  age  of  forty-five  years  menstruation 
ceases  :  this  is  the  menopause,  or  climacteric,  or  change 
of  life.  The  cessation  is  not  abrupt,  but  gradual. 
The  menstruation  becomes  irregular,  and  finally  ceases 
altogether. 

Composition  of  Menses. — The  menstrual  flow  is  com- 
posed of  blood  from  the  uterine  blood-vessels.  Some 
authorities  think  some  of  the  blood  is  from  the  Fallo- 
pian tubes.  Whether  there  is  also  present  the  broken- 
down  mucous  membrane  of  the  uterus  or  simply  exfoli- 
ated epithelium  is  still  a  mooted  question. 

The  changes  which  take  place  in  the  mucous  mem- 
brane of  the  body  of  the  uterus  during  menstruation 
are  not  agreed  upon  by  authorities.  Some  hold  to  the 
view  that  the  entire  membrane,  down  to  the  muscular 
coat,  is  thrown  off;  others  that  only  the  epithelial  layer 
is  cast  off;  while  still  others  think  that  even  this  slight 
amount  of  destruction  is  absent.  J.  Bland  Sutton  main- 
tains that  there  is  no  discharge  of  mucous  membrane, 
basing  his  opinion  upon  observations  he  made  on  the 


REPRODUCTIVE  FUNCTIONS. 


349 


macaque  monkey,  in  which  animal  there  seems  to  be  a 
true  menstruation.  The  evidence  seems  to  support  the 
theory  that  the  extent  to  which  tissue  is  destroyed  is  no 
greater  than  involves  the  epithelium. 


Fig.  96 — Uterus  during  Menstruation  (Courty),  cut  open  to  show  the  swelling  of  the 
whole  organ,  and  particularly  the  mucous  membrane:  /4  ,  mucous  membrane  of  cer- 
vix ;  B,  C,  mucous  membrane  of  corpus,  much  thickened;  D,  muscular  layer;  E, 
uterine  opening  of  tube  ;  F,  os  internum  (the  mucous  membrane  tapers  down  to 
these  openings). 

Cause  of  Menstruation. — The  cause  of  menstruation  is 
still  undetermined.  Some  writers  regard  it  as  dependent 
on  a  special  nerve-centre.  It  is  claimed  that  in  the  re- 
moval of  the  ovaries  and  tubes  to  produce  a  premature 
menopau.se,  as  is  done  by  surgeons  for  certain  diseased 
conditions,  this  is  more  certainly  accomplished  if  a  large 


350  HUMAN  PHYSIOLOGY. 

nerve-trunk  which  hes  in  the  angle  between  the  round 
hgament  and  the  tube  is  included  in  the  ligature,  so  as 
to  destroy  its  function ;  but  the  evidence  on  this  point  is 
not  convincing. 

Relation  between  Ovulation  and  Menstruation. — The 
relation  between  these  two  processes  is  as  yet  undeter- 
mined, although  physiologists  in  the  main  hold  that  at 
the  time  of  the  discharge  of  an  ovum  from  the  ovary 
there  is  such  a  condition  of  the  uterus  as  brings  about 
its  increased  vascularity  and  the  oozing  from  its  vessels 
of  the  menstrual  blood.  They  believe  that  at  each 
menstruation  there  is  discharge  of  an  ovum.  Other 
writers — and  these  are  principally  surgeons  who  have 
devoted  much  time  to  the  study  of  diseases  of  women, 
and  who  have  large  experience  in  operations  for  the 
removal  of  the  ovaries — differ  very  materially  from  the 
physiologists.  One  of  the  number  (A.  Reeves  Jackson, 
in  an  article  entitled  "  Ovular  Theory  of  Menstruation : 
Will  it  Stand?"  in  the  American  Journal  of  Obstetrics) 
says :  "  Menstruation  may  occur  without  accompanying 
ovulation ;  ovulation  may  occur  without  accompanying 
menstruation;  and  ovulation  is  the  irregular  but  constant 
function  of  the  ovaries,  while  menstruation  is  the  regular 
rhythmical  function  of  the  uterus."  Lawson  Tait,  the 
celebrated  surgeon,  says  that "  ovulation  and  menstruation 
are  not  only  not  concurrent,  but  ovulation  is  much  less 
frequent  than  menstruation."  J.  Bland  Sutton,  already 
referred  to,  says :  "  It  is  very  difficult  to  uproot  ancient 
tradition,  especially  one  so  ancient  as  the  belief  in  the 
intimate  association  of  ovulation  and  menstruation,  but 
evidence  is  rapidly  accumulating  which  will  show  that 
the  two  processes  are  not  so  intimately  connected  as  was 
formerly  supposed." 


PLATE     IV. 


Fie;.  I.— Ovary  of  Woman  two  days  after  Menstruation,  showing  earliest  stages  of  transformation 
of  a  ruptured  and  bloody  Graafian  follicle  into  a  corpus  luteum. 

Fig.  2. — Ovary  of  Woman  nine  days  after  Menstruation:  The  dark  spot  is  the  cicatrice;  the  sur- 
rounding yellow  circle  is  the  corpus  luteum  shining  through  the  transparent  tissue. 

Fio.  i. — Ovary  of  Woman  at  term  of  Pregnancy,  showing  corpus  luteum  wiih  firm  white  central 
clot. 

Fig.  4.— (.)vary  of  Woman  twenty  days  after  Menstruation  :  Besides  large  fresh  corpus  luteum  are 
seen  two  smaller  old  ones,  and  Graafian  follicles  of  different  sizes  {Daltok). 


REPRODUCTIVE  FUNCTIONS.  35  I 

It  would  appear,  then,  that  the  relation  existing  be- 
tween ovulation  and  menstruation  is  not  definitely  deter- 
mined, but  that  they  are  in  some  manner  associated 
cannot  be  questioned,  for  the  removal  of  the  ovaries,  as 
a  rule,  is  followed  by  a  discontinuance  of  menstruation. 

Formation  of  Corpus  Lntcnin  (PI.  4). — After  an  ovum  is 
discharged  from  a  Graafian  vesicle  certain  changes  take 
place  in  the  latter  structure,  which  changes  result  in  the 
formation  of  a  corpus  luteum.  The  cavity  of  the  vessel 
is  filled  with  blood  which,  like  blood  elsewhere,  coag- 
ulates. The  serum  becomes  expressed  from  the  clot, 
and  is  absorbed,  and  later  the  clot,  which  at  first  was  red, 
becomes  decolorized.  The  membrana  propria  becomes 
thickened  and  convoluted,  especially  opposite  the  point 
at  which  the  ovum  escaped,  and  subsequently  becomes 
of  a  yellow  color  ;  whence  its  name.  This  body  becomes 
smaller  and  smaller  and  finally  disappears.  As  a  corpus 
luteum  forms  whenever  a  vesicle  ruptures,  it  is  no  evi- 
dence of  pregnancy.  If  impregnation  take  place,  the 
corpus  luteum  becomes  larger  and  remains  for  a  longer 
time  than  when  pregnancy  does  not  occur.  The  length 
of  time  required  for  the  descent  of  the  ovum  to  the 
uterus  is  unknown,  but  is  believed  to  be  about  seven 
days.  During  the  passage  it  receives  a  covering  of 
albuminous  material  from  the  mucous  membrane  of  the 
tube. 

Maturation  of  the  Ovum. — The  changes  which  take 
place  in  the  ovum  itself  during  the  descent  have  been 
studied  in  lower  animals,  and  it  is  inferred  that  the  same 
changes  occur  in  the  human  ovum  ;  they  constitute  the 
maturation  of  the  ovum.  To  understand  these  changes 
thoroughly  it  is  necessary  to  be  familiar  with  karyo- 
kinesis,  the  process  of  indirect    division  of  the    nuclei 


352 


HUMAN  PHYSIOLOGY. 


of  cells.  The  ovum  is  a  cell  whose  nucleus  is  the 
germinal  vesicle,  and  the  nucleolus  is  the  germinal  spot. 
The  germinal  vesicle  has  its  enclosing  membrane,  the 
nuclear  membrane,  and  the  protoplasm  of  the  vesicle  is 


Fig.  97. — Karyokinesis,  or  Indirect  Cell-division:  a,  cell  with  nucleus  in  quiescent  state 
(the  nucleus  contains  nucleoli  and  a  network  of  threads) ;  b,  formation  of  coarse  chro- 
matin threads  in  nucleus;  c,  disappearance  of  nucleolus  and  membrane  of  nucleus; 
arrangement  of  threads  in  loops,  forming  the  "  rosette;  "  d,  angles  of  loops  directed 
toward  the  poles  of  the  cell,  which  are  formed  of  achromatic  threads ;  e,  beginning 
division  of  the  cell ;  this  is  followed  by  a  gradual  return  of  the  nucleus  to  the  quies- 
cent state  (a). 

reticulated.  This  vesicle  approaches  the  surface  of  the 
ovum,  and  as  a  result  of  several  changes  that  take  place 
in  it  a  polar  globule  is  formed,  and  later  a  second  one. 
These  globules  have  no  further  office,  but  what  remains 
of  the  vesicle  after  their  separation  returns  to  the  centre 


REPRODUCTIVE   FUXCTIONS.  353 

of  the  ovum,  and  now  receives  the  name  of"  female  pro- 
nucleus." It  is  to  be  understood  that  the  changes  in  the 
ovum  which  have  been  described  occur  entirely  inde- 
pendently of  impregnation ;  indeed,  it  is  questionable 
whether  an  ovum  can  be  considered  as  mature  until  the 
stage  has  been  reached  in  which  the  female  pronucleus 
has  been  formed. 

Impregnation. — During  coitus,  or  sexual  intercourse, 
the  seminal  fluid  is  forcibly  thrown  into  the  vagina,  and  by 
virtue  of  their  vibratile  movements  the  spermatozoa  enter 
the  canal  of  the  cervix  uteri  and  pass  through  the  canal  of 
the  body  into  the  Fallopian  tube,  in  which  it  is  believed 
that  they  meet  the  ovum  in  its  descent,  probably  in  the 
upper  portion.     Here  fecundation  or  impregnation  occurs. 

It  was  formerly  held  that  the  spermatozoa  might  fer- 
tilize the  ovum  while  the  latter  was  still  in  the  ovary, 
and  that  its  development  there,  more  or  less  complete, 
constitutes  ovai'ian  pregnancy,  and  also  that  in  some 
instances  the  ovum  so  impregnated,  instead  of  going 
through  with  development  in  the  ovary,  might  drop  into 
the  abdominal  cavity,  and  there  develop,  constituting  ab- 
dominal pregnancy  ;  but  the  present  view  is  that  ovarian 
pregnancy  rarely  occurs,  if  ever,  and  that  abdominal 
pregnancy  results  from  the  rupture  of  a  Fallopian  tube 
in  which  an  impregnated  ovum  has  previously  lodged 
and  developed.  If  this  view  be  correct,  every  extra- 
uterine pregnancy  resolves  itself  originally  into  a  tubal 
pregnancy,  and  fertilization  of  the  ovum  always  takes 
place  in  the  tube,  probably  in  the  upper  portion,  for  it  is 
probable  that  the  layer  of  albuminous  material  added  to 
the  exterior  of  the  ovum  by  the  mucous  membrane  of  the 
Fallopian  tube  in  the  lower  part  of  the  canal  would  serve 
as  an  ob.stacle  to  the  entrance  of  the  spermatozoa. 

2a 


354 


HUMAN  PHYSIOLOGY. 


Method  of  Fertilization. — In  the  vitelline  membrane  of 
the  ova  of  some  animals  there  is  a  minute  opening  called 
the  "  micropyle,"  by  which  a  spermatozoon  gains  access 
to  the  interior.     Such  an  opening  does  not  exist  in  the 


Fig.  98.— Sections  of  the  Ovum  of  a  Rabbit,  showing  the  formation  of  the  blastodermic 
vesicle  (E.  Van  Beneden):  a,  b,  c,  d,  are  ova  in  successive  stages  of  development; 
zp,  zona  pellucida;  ect,  ectomeres,  or  outer  cells  ;  ent,  entomeres,  or  inner  cells. 

human  ovum.  Some  histologists  have  described  the 
vitelline  membrane  as  possessing  a  porous  structure,  and 
it  has  been  suggested  that  through  one  of  these  pores  a 


REPRODUCTIVE  FUNCTIONS.  355 

spermatozoon  niig^ht  pass.  It  is  by  no  means  established 
that  such  pores  exist.  However,  in  some  way  the  sper- 
matozoon passes  through  the  membrane  into  the  proto- 
plasm; here  its  tail  disappears  and  the  head  assumes  a 
spherical  form,  and  to  it  the  name  of  "  male  pronucleus  " 
is  given.  The  male  and  female  pronuclei  then  unite  to 
produce  the  "fecundation  nucleus."  After  this  occurs  the 
ovum  consists  of  a  mass  of  protoplasm  with  a  nucleus, 
and  is  spoken  of  as  the  "  segmentation  sphere,"  because 
it  undergoes  segmentation. 

Segmentation. — This  consists  in  the  production  of  two 
segments  by  the  same  process  of  indirect  division  which 
took  place  in  the  germinal  vesicle ;  these  again  divide, 
forming  four,  and,  the  same  process  continuing,  the  en- 
tire ovum  is  broken  up  into  a  mass  of  spherical  cells 
which,  from  the  resemblance  to  a  mulberry,  is  named 
"morula."  These  cells  separate  into  two  layers  with  fluid 
between  them,  except  at  one  place  where  the  two  layers 
are  in  contact.  The  blastodermic  vesicle  is  now  formed. 
It  is  probable  that  development  has  reached  this  stage  at 
about  the  tenth  day,  by  which  time  the  ovum  has  entered 
the  uterus.  The  albuminous  secretion  of  the  Fallopian 
tube  serves  as  pabulum  or  food  to  the  cells  in  this  process. 

Formation  of  Embryo. — The  next  change  which  takes 
place  is  the  formation  of  three  layers  from  the  two  just  de- 
scribed. They  are  termed  the  cpiblast,  the  uicsoblast,  and 
the  hypoblast ;  together  they  form  the  blastoderm.  The 
epiblast  is  most  external,  in  contact  with  the  vitelline  mem- 
brane, which  takes  no  part  in  the  changes  thus  far  described. 

It  would  perhaps  be  too  much  to  say  that  the  embryo 
is  now  formed,  yet  the  subsequent  changes  are  but  the 
modification  and  differentiation  of  the  cells  which  com- 
pose these  three  layers.     The  epiblast  forms  the  brain 


356  HUMAN  PHYSIOLOGY. 

and  spinal  cord,  portions  of  the  organs  of  special  sense, 
and  the  epidermis,  and  also  takes  part  in  the  formation 
of  the  chorion  and  amnion.  The  mesoblast  forms  the 
vascular,  osseous,  and  muscular  systems  and  the  endo- 
thelium which  lines  the  serous  cavities.  The  hypoblast 
forms  the  lungs,  the  epithelium  of  the  alimentary  canal 
and  of  the  glands  which  are  offshoots  from  this  canal. 
The  membrane  which  lines  the  allantois  and  the  yolk- 
sac  are  also  formed  from  the  hypoblast. 

The  segmentation  just  described  is  such  as  takes 
place  in  the  human  ovum  and  that  of  other  mammalia. 
It  is  a  process  in  which  the  entire  mass  of  protoplasm 
undergoes  division :  such  ova  are  said  to  be  "  holoblastic." 
In  the  ova  of  birds  and  of  reptiles  only  a  portion  under- 
goes this  segmentation,  the  rest  serving  as  food.  Such 
ova  are  "  mesoblastic."  As  an  illustration  of  the  latter 
may  be  mentioned  the  fowl's  &2,'g,  in  which  the  processes 
of  development  have  most  thoroughly  been  studied.  In 
this  &^^  only  a  minute  portion,  the  cicatricula,  becomes 
converted  into  the  chick,  while  the  great  body  of  material 
nourishes  the  growing  embryo  until  it  leaves  the  shell 
and  is  able  to  gain  its  own  livelihood.  As  such  an  em- 
bryo is  never  attached  to  the  parent,  it  must  have  within 
itself  all  the  material  necessary  for  its  development  and 
maintenance  until  freed  from  its  enclosing  shell,  hence 
the  large  size  of  the  ovum ;  while  in  the  mammal  this 
supply  is  not  necessary,  for  the  attachment  to  the 
maternal  structures  is  made  at  an  early  period  of  its 
history,  and  from  the  parent  all  necessary  sustenance  is 
obtained. 

Inasmuch  as  development  has  been  so  much  more 
thoroughly  studied  in  the  hen's  &^^  than  in  any  other, 
and   inasmuch    as  the  processes  are  in  many  respects 


REPRODUCTIVE    FUNCTIONS.  357 

probably  the  same  as  in  the  human  ovum,  the  develop- 
ment of  the  chick  will  be  described,  referring  to  the 
principal  points  of  difference  as  they  are  reached  in  the 
description,  giving,  however,  only  a  general  view  of  the 
subject,  which  is  much  too  extensive  and  complicated  to 
discuss  in  any  other  manner  in  this  connection. 

Development  of  Chick. — If  the  shell  of  a  hen's  Gigg  be 
broken  during  the  first  day  of  its  incubation  and  the 
blastoderm  be  examined,  it  will  be  seen  that  there  is  a 
clear  central  portion,  the  area  pellucida,  and  a  portion 
outside  of  this,  the  area  opaca,  which  is  much  less  clear. 
The  embryo  forms  in  the  area  pellucida,  and  the  mem- 
branes and  structures  which  are  to  nourish  it  form  in  the 
area  opaca.  On  the  second  day,  the  area  opaca  having 
meanwhile  extended,  within  it  are  formed  red  blood-cor- 
puscles and  vessels,  and  during  the  same  time  in  the  area 
pellucida  the  heart  is  formed.  These  structures  arise,  as 
has  been  stated,  from  the  cells  of  the  mesoblast. 

At  one  extremity  of  the  area  pellucida  a  fold  forms 
in  the  blastoderm,  and,  as  this  is  the  anterior  end,  it  is 
called  the  "  cephalic  fold."  A  similar  fold,  the  tail  fold, 
forms  at  the  other  extremity  of  the  area  pellucida.  In 
the  same  manner  lateral  folds  form  on  the  sides.  All 
these  folds,  which  include  the  three  layers  of  the  blasto- 
derm, approach  one  another  below,  and  by  so  doing 
form  a  canal,  the  embryonal  sac.  This  sac  is  bounded 
above  by  the  blastoderm,  anteriorly  by  the  cephalic  fold, 
po.steriorly  by  the  tail  fold,  and  laterally  by  the  lateral 
folds,  while  below  it  is  in  communication  with  the  vitel- 
lus.  This  embryonal  sac  subsequently  becomes  divided 
into  two,  one  division  forming  the  alimentary  tract  and 
the  other  the  body-walls,  the  umbilicus  being  the  point 
at  which  the  folds  all  unite.     These  folds  just  described 


358  HUMAN  PHYSIOLOGY. 

are  to  be  carefully  distinguished  from  the  membranes, 
the  amnion,  the  chorion,  etc.  The  folds,  as  stated,  in- 
volve the  epiblast,  the  mesoblast,  and  the  hypoblast, 
while  in  the  formation  of  the  membranes  the  various 
layers  play  different  parts. 

Membranes  of  the  Ejubryo. — Amnion. — The  mesoblast 
about  the  embryo  splits  into  two  laminae,  the  parietal  and 
the  visceral.  The  parietal  (external)  joins  with  the  epi- 
blast to  form  the  somatoplcnre,  from  which  the  amnion  and 
the  body-walls  are  developed,  while  the  visceral  lamina 
unites  with  the  hypoblast  to  form  the  splanchnopleure. 
From  this  structure  are  developed  the  walls  of  the  allan- 
tois,  the  yolk-sac,  and  the  alimentary  canal.  Between 
the  somatopleure  and  the  splanchnopleure  is  the  pleuro- 

ATC. 

V. 

-"  ^^    RSo. 


Fig.  99. — Diagrammatic  Longitudinal  Section  through  the  Axis  of  an  Embryo  Chick 
(Foster  and  Balfour):  N.  C,  neural  canal;  C/i,  notochord ;  D,  foregut ;  I^.  So, 
somatopleure  ;  J^.  Sp,  splanchnopleure  ;  Sp,  splanchnopleure  forming  the  lower  wall 
of  the  foregut  ;  Ht.  heart;  pp,  pleuropentoneal  cavity;  Am,  amniotic  fold;  A,  epi- 
blast ;  B,  mesoblast ;   C,  hypoblast. 

peritoneal  cavity,  which  later  is  divided  by  partitions 
into  pericardial,  pleural,  and  peritoneal  cavities.  From 
the  somatopleure  folds  form  which  rise  above  the  em- 
bryo on  all  sides,  meeting  over  its  back  and  fusing 
together.  These  are  the  amniotic  folds.  As  each  fold 
is  double,  when  they  unite  two  membranes  result :  the 


REPRODUCTIVE  FUNCTIONS.  359 

inner,  next  the  embryo,  is  the  amnion,  and  the  outer, 
toward  the  vitelhne  membrane,  is  the  false  amnion  (Fig. 
100).     The  amnion  and  the  vitelline  membrane  fuse  to- 


FiG.  100. — Diagrammatic  Longitudinal  Section  of  a  Chick  on  the  Fourth  Day  (Allen 
Thomson):  <■/,  epitilast ;  hy,  hypoblast;  sm,  somatopleure  ;  vin,  splanchnopleure  ; 
of,  p/,  folds  of  the  amnion  ;  //,  pleuro-peritoneal  cavity ;  am,  cavity  of  amnion  :  ai, 
allantois  ,  a,  position  of  the  future  anus  ;  h,  heart  ;  /,  intestine  ;  zii,  vitelline  duct  ; 
ys,  yolk  ;  s,  foregut ;  m,  position  of  the  mouth  ;  me,  the  mesentery. 

gether,  forming  the  chorion.  The  true  amnion  has  epi- 
blast  for  its  inner  and  mcsoblast  for  its  outer  layer,  and 
the  space  between  it  and  the  embryo  is  the  amniotic 
cavity,  in  which  the  liquor  amnii  accumulates. 

Yolk-sac. — The  yolk-sac  is  a  very  important  structure 
in  the  fowl  and  in  birds  generally,  as  it  is  upon  the  yolk 
that  the  nutrition  of  the  embryo  depends ;  but  in  mam- 
mals it  is  of  little  importance,  as  the  nutritive  material 
in  the  vitellus  is  insignificant  in  amount. 

Allantois. — The  allantois  is  a  projection  of  the  splanch- 
nopleure into  the  pleuro-peritoneal  cavity.  It  subse- 
quently communicates  with  the  posterior  portion  of  the 
intestinal  canal,  and  its  lining  is  hypoblast.  This  struc- 
ture projects  more  and  more  into  the  pleuro-peritoneal 
cavity,  following  up  the  folds  that  have  been  described 
as  forming  the  true  and  the  false  anmion.  The  allantois 
at  last  comes  in  contact  with  the  chorion,  which,  it  will  be 


360  HUMAN  PHYSIOLOGY. 

remembered,  was  formed  by  the  fusion  of  the  false  am- 
nion with  the  vitelline  membrane,  and  into  the  villi  of 
that  structure  it  sends  processes.  It  is  especially  devel- 
oped in  the  part  corresponding  to  the  attachment  of  the 
ovum  to  the  uterine  wall.  The  allantois  has  two  layers, 
a  mesoblastic  and  a  hypoblastic.  In  the  former  are 
blood-vessels  which  come  from  the  vascular  system  of 
the  embryo,  the  connecting  vessels  becoming  the  umbil- 
ical arteries.  At  a  later  stage  of  development  the  cavity 
of  the  allantois  disappears,  except  in  that  portion  which 
is  to  be  included  within  the  body  of  the  foetus,  and  which 
becomes  the  urinary  bladder,  and  in  that  portion  be- 
tween the  bladder  and  the  umbilicus,  which  becomes 
the  urachus. 

Chorion. — This  membrane,  as  already  stated,  is  formed 
by  the  union  of  the  vitelline  membrane  and  the  false 
amnion.  When  first  formed,  it  is  smooth,  but  becomes 
shaggy  by  the  growth  from  it  of  processes  called  "villi." 
These  villi  are  at  first  scattered  over  the  whole  exterior 
of  the  ovum,  but  later  they  are  found  only  at  the  point 
of  attachment  of  the  ovum  to  the  uterus,  where  the 
placenta  is  to  be  formed.  In  these  villi  are  blood- 
vessels from  the  foetal  vascular  system. 

Placenta. — When  the  impregnated  ovum  reaches  the 
cavity  of  the  uterus  the  mucous  membrane  of  that  organ 
is  prepared  to  receive  it,  and  it  finds  a  lodgement  there. 
Under  the  stimulus  of  impregnation  the  whole  mu- 
cous membrane  becomes  thickened,  and  at  the  termina- 
tion of  utero-gestation  the  entire  mucous  membrane  of 
the  body  is  cast  off;  it  is  called  the  "  decidua  vera." 
Especially  marked  is  this  thickening  at  the  point  of 
attachment  of  the  ovum,  and  to  this  part  the  name 
"  decidua  serotina"  is  applied  (Fig.  lOi).     As  a  result  of 


REPRODUCTIVE  FUNCTIONS. 


361 


this  stimulus  the  mucous  membrane  increases  around 
the  ovum,  finally  completely  enclosing  it.  This  new  for- 
mation is  the  "  decidua 
reflexa." 

The  villi  of  the  cho- 
rion find  their  way  into 
the  depressions  of  the 
decidua  serotina,  and 
their  walls  become  atro- 
phied, being  finally  rep- 
resented only  by  epi- 
thelial cells  covering  the 
capillary     blood-vessels 

which     have    come    from     Fir,.  loi.— Series  of  Diagram.s  representing  the 

Relationship  of  the  Decidua  to  the  Ovum  at 
Different  Periods.  The  decidua  are  colored 
black,  and  the  ovum  is  shaded  transversely. 
In  4  and  5  the  vascular  processes  of  the  chorion 
are  figured.  {Copied  frojit  Daiion.)  i,  ovum 
entering  the  congested  mucous  membrane  of 
the  fundus — decidua  serotina  ;  2,  decidua  re- 
flexa growing  around  the  ovum  ;  3,  completion 
of  the  decidua  around  the  ovum  ;  4,  general 
growth  of  villi  of  the  chorion ;  5,  special 
growth  of  villi  at  placental  attachment,  and 
atrophy  of  the  rest. 


theallantois.  The  blood- 
vessels in  the  decidua  se- 
rotina become  converted 
into  blood-spaces,  sinus- 
es, to  which  the  uterine 
arteries  carry  blood,  and 
from  which  the  uterine 
veins  carry  the  blood 
away.  It  will  be  seen,  therefore,  that  the  foetal  blood-ves- 
sels are  surrounded  by  the  maternal  blood  in  the  uterine 
sinuses,  the  two  fluids  being  separated  only  by  the  thin 
wall  of  the  fcetal  capillaries,  through  which  the  inter- 
changes of  oxygen  and  carbon  dioxide  take  place,  and 
also  the  passage  of  the  nutritious  material  to  supply  the 
growing  fcetus,  and  in  the  reverse  direction  pass  the  effete 
products  to  be  eliminated.  The  structure  which  performs 
all  these  important  offices  is  the  placenta,  made  up  of  both 
maternal  and  frjetal  tissues.  It  seems  hardly  necessary 
to  say  that  the  blood  of  the  mother  and  that  of  the  child 


362  HUMAN  PHYSIOLOGY. 

never  come  in  contact,  but  are  always  separated  by  the 
walls  of  the  foetal  capillaries. 

At  birth  the  placenta  is  cast  off,  and  in  the  contraction 
of  the  uterine  muscular  tissue  the  mouths  of  the  maternal 
blood-vessels  are  closed,  and  thus  hemorrhage  is  pre- 
vented. The  blood  which  escapes  during  a  normal  labor 
is  that  which  was  in  the  sinuses.  The  functions  of  the 
placenta  are  thus  seen  to  be  threefold — nutritive,  respi- 
ratory, and  excretory. 

Circulation  in  the  Embryo. — -  Vitelline  Circtilation. — 
During  the  earliest  weeks  of  human  foetal  life  the  con- 
tents of  the  ovum  supply  the  growing  embryo  with 
nutrition.  This  is  done  by  means  of  vessels  which  com- 
pose the  vitelline  circulation,  but,  important  as  this  cir- 
culation is  in  the  fowl's  &gg,  it  is  of  very  brief  duration 
in  the  human  subject,  for  the  supply  of  nutritious  ma- 
terial is  soon  exhausted,  probably  at  the  sixth  week. 

Placental  or  Foeial  Circulation. — By  the  sixth  week  the 
placenta  is  formed  and  the  connection  has  been  made 
by  which  the  embryo  receives  its  nourishment  from  the 
maternal  blood.  From  this  time  until  birth  the  foetus 
depends  upon  the  placental  or  foetal  circulation  for  its 
nourishment  and  maintenance. 

The  blood  of  the  foetus  is  freed  from  much  of  its  im- 
purities in  the  placenta,  and  there  likewise  it  receives 
oxygen  and  nutritive  materials.  It  returns  to  the  foetus 
through  the  umbilical  vein,  passing  to  the  liver.  In  this 
organ  the  current  is  divided :  the  greater  part  joins 
with  the  venous  blood  of  the  portal  vein;  a  second 
portion  goes  directly  into  the  hepatic  circulation ;  while 
a  third  part  goes  through  the  ductus  venosus  into  the 
ascending  vena  cava  without  passing  through  the  liver. 
The  currents  all  meet  again  in  the  ascending  vena  cava, 


REPRODUCTIVE  FUNCTIONS. 


363 


here   mixing  with  the   blood  returning  from  the  lower 
extremities.      The   ascending  vena   cava   discharges  its 


R.Con.CaioCidt 

;         L  Com  Cuyohd 


t/mbiUcu 


-£xt  Iliae 


Placenta, 

Fm.  102. — Diagram  of  the  FcEtal  Circulation. 

blood  into  the  right  auricle  of  the  heart,  where,  guided 
by  the  Eustachian  valve,  it  is  directed  into  the  left  auricle 


364  HUMAN  PHYSIOLOGY. 

through  the  foramen  ovale.  From  this  cavity  it  passes 
into  the  left  ventricle,  thence  into  the  aorta,  which  dis- 
tributes it  to  the  head  and  upper  extremities.  It  will  be 
seen  from  this  description  that  to  these  three  portions 
of  the  body  the  blood  from  the  placenta  is  distributed. 
This  blood  is  not  very  pure,  for  it  has  been  deteriorated 
by  the  impure  blood  returning  from  the  lower  extrem- 
ities, with  which  it  mixes  in  the  ascending  vena  cava ; 
but  it  is  the  purest  and  most  nutritious  blood  the  foetus 
receives,  and  this  accounts  for  the  greater  development 
of  the  upper  portion  of  the  body  as  compared  with  the 
lower,  which  is  so  striking  a  feature  in  the  new-born 
babe. 

The  blood  returns  from  the  head  and  upper  extrem- 
ities through  the  descending  vena  cava  to  the  right  auri- 
cle, and  thence  passes  into  the  right  ventricle.  There  is 
probably  always  a  slight  mixing  of  the  currents  in  the 
right  auricle,  that  returning  from  the  placenta  and  that 
from  the  descending  vena  cava,  but  at  first  this  is  very 
slight ;  later  it  is  doubtless  greater.  From  the  right 
ventricle  the  blood  passes  into  the  pulmonary  artery, 
a  very  small  portion  going  through  the  capillaries  of 
the  lungs,  the  larger  part  passing  through  the  ductus 
arteriosus  into  the  aorta,  passing  down  this  vessel  to  the 
internal  iliac,  from  which  are  given  off  the  hypogastric 
or  umbilical  arteries  by  which  the  blood  is  conveyed  to 
the  placenta. 

By  comparing  this  description  with  that  of  the  circu- 
lation in  the  adult  the  points  of  difference  will  be  seen. 
It  may  be  well  to  note  here  that  there  are  six  principal 
points  of  difference  between  the  foetal  and  the  adult  cir- 
culatory apparatus,  besides  less  important  ones  of  size 
and  shape.     These  points  of  difference  are  the  presence 


REPRODUCTIVE   FUNCTIONS.  365 

in  the  foetal  heart  of  the  Eustachian  valve  and  the  for- 
amen ovale,  in  the  venous  system  of  the  umbilical  vein 
and  the  ductus  venosus,  and  in  the  arterial  system  of  the 
umbilical  arteries  and  the  ductus  arteriosus. 

Changes  in  the  Circulation  at  Birth. — During  intra- 
uterine life  the  respiratory  centre  in  the  medulla  is  sup- 
plied with  blood  containing  sufficient  oxygen  to  prevent 
any  inspiratory  impulse,  and  there  is  therefore  during 
this  period  no  attempt  at  respiration  on  the  part  of  the 
foetus.  (See  Resistance  Theory  of  Respiration,  p.  251.) 
As  soon,  however,  as  the  connection  between  the  parent 
and  the  child  is  severed,  whether  by  separation  of  the 
placenta  or  by  tying  of  the  umbilical  cord,  the  respi- 
ratory centre,  being  no  longer  supplied  with  oxygen, 
sends  out  impulses  to  the  respiratory  muscles,  and  res- 
piration begins.  This  may  be  hastened  or  assisted  by 
slapping  the  skin  or  dashing  water  upon  it,  but  under 
ordinary  circumstances  these  measures  are  not  called 
for.  The  fact  that  respiration  will  take  place  while  the 
foetus  is  still  enclosed  in  its  membranes,  without  the 
reflex  influence  of  exposure  to  the  air,  shows  that  this  is 
not  the  essential,  but  only  a  contributing,  cause.  It  is 
the  stoppage  of  the  placental  circulation  which  starts 
the  respiratory  movements. 

Although  during  foetal  life  some  blood  flows  through 
the  pulmonary  capillaries,  still  the  amount  is  small,  and, 
there  being  no  air  in  the  pulmonary  alveoli,  the  lungs 
will  sink  if  placed  in  water.  The  first  respiratory  move- 
ment causes  an  enlargement  of  the  thoracic  cavity  and 
a  consequent  distention  of  the  lungs,  the  air  passing 
into  the  alveoli,  and  the  blood,  which  is  at  the  same 
time  in  the  pulmonary  capillaries,  becomes  o.xygenated 
and  returns  to  the   left  auricle  as  arterial  blood.     The 


366  HUMAN  PHYSIOLOGY. 

expansion  of  the  thorax  reduces  the  resistance  to  the 
flow  of  the  blood  through  the  pulmonary  circulation, 
and  as  a  result  a  large  amount  of  blood  goes  to  the 
lungs;  this  means  a  lessened  amount  through  the  ductus 
arteriosus,  and,  following  the  law  that  a  diminution  of 
function  is  followed  by  atrophy,  this  vessel  begins  to 
diminish  in  size,  and  becomes  closed  between  the  fourth 
and  tenth  days,  and  in  later  life  is  to  be  found  as  a  fibrous 
cord  between  the  left  pulmonary  artery  and  the  aorta. 

With  the  termination  of  the  placental  circulation  the 
flow  through  the  ductus  venosus  ceases,  and  within  a  few 
days  this  vessel  closes,  and  remains  only  as  a  fibrous  cord 
in  the  fissure  of  the  same  name  in  the  liver :  that  portion 
of  the  umbilical  vein  which  is  within  the  body  of  the  child 
becomes  the  round  ligament  of  the  liver.  The  blood 
flowing  into  the  right  auricle  from  the  inferior  vena  cava 
finds  it  easier  to  pass  into  the  right  ventricle  than  into 
the  left  auricle,  which  is  now  filled  with  blood  from  the 
lungs,  and  hence  takes  this  course,  while  the  blood  can- 
not flow  into  the  right  auricle  through  the  foramen  ovale 
by  reason  of  the  valve  which  has  been  forming  in  the 
left  auricle  during  the  latter  part  of  intra-uterine  life  to 
close  this  opening.  The  opening  is  not  permanently 
closed  for  a  considerable  time  after  birth,  in  some  cases 
a  year,  and  sometimes  not  at  all.  As  a  result  of  these 
various  changes  the  foetal  circulation  becomes  converted 
into  that  of  the  adult. 


INDEX 


Abdominal  pregnancy,  353 
Abducens  nerve,  289 
paralysis  of,  290 
Absorption,  131 

action  of  villi  of  intestine  in,  132 
of  fat,  135 
of  food,  92 
Absorptive  powers  of  large  intestine, 

129 
Accommodation,  315 
Acetic  acid,  53 
Acetone,  53 
Achroodextrin,  conversion  of  starch 

into,  46 
Acid,  acetic,  53 

carbonic,  in  body,  41 
fatty,  53 
formic,  53 

hydrochloric,  in  body,  41 
Acid-albumin,  59 
Acuteness  of  sense  of  smell,  303 
Afferent  nerves,  224 
Age,   influence    of,    on    temperature, 

167 
Air,  density  of,  in  lungs,  157 
expired,  composition  of,  160 
impure,    influence    of,    on    health, 
161 
Albuminoids,  66 
Albumins,  derived,  59 
acid-,  59 
alkali-,  60 
casein,  61 
syntonin,  60 
native,  59 

egg-.  59 
serum,  59 
Albumoses,  64 
importance  of,  65 


Alcohol,  action    of,  on  nervous  sys- 
tem, 116 
on  stomach,  1 17 
on  vascular  system,  116 
effect  of,  on  animal  tissues,  116 

on  digestion,  115 
influence  of,  on  temperature,  Il6 
value  of,  in  digestion,  115 
Alcoholic  fermentation  of  dextrose,  48 
Alkali-albumin,  60 
Alkaline  phosphates,  34 

avenues  of  discharge  of,  35 
office  of,  34 
source  of,  35 
Alkalinity  of  blood-plasma,  34 
Allantois,  359 
Ammetropia,  318 
Ammonia  in  body,  41 
Ammonium  salts  in  body,  40 
Amnion,  358 
Amylo-dextrin,  45 
Amylolytic  enzyme  (ferment),  71 
Amylopsin,  72,  125 

in  pancreatic  juice,  45 
Animal  tissues,  effect  of  alcohol  on, 

116 
Appendages  of  eye,  321 
Arnold's     ganglion     of     trigeminus 

nerve,  289 
Arterial  pressure,  185 

supply  to  eye,  312 
Arteries,  174 

circulation  of  blood  in,  183 
rate  of  flow  of  blood  in,  185 
Asphyxia,  253 

convulsion  in,  253 
dyspnoea  in,  253 
exhaustion  in,  253 
inspiratory  spasm  in,  253 
Aspiration  of  thorax,   effects    of,  on 
circulation  of  blood,  188 

367 


368 


INDEX. 


Astigmatism,  319 

Atlieroma  due  to  vegetarianism,  89 

Auditory  centre  of  brain,  274 

nerve,  292 
Auricular  diastole,  177 

systole,  176 
Auricles  of  heart,  170 
Automatic  centres  of  medulla  oblon- 
gata, 251 

B. 

Basal  ganglia  of  brain,  264 
Baths  in  care  of  skin,  204 
Bile,  123 

action  of,  in  absorption  of  fat,  135 

on  chyme,  127 
composition  of,  124 
disintegration  of,  128 
in  emulsification,  128 
in  intestinal  digestion,  123 
mucin  in,  67 
quantity  secreted,  124 
Bile-acids,  Pettenkofer's  test  for,  75 
Bilirubin,  80 
Bilivirdin,  80 

Gmelin's  test  for,  80 
Birth,  changes  in  circulation  at,  365 
Bladder,  control  of  brain  on  evacu- 
ation of,  244 
control  of  nerve-centres  on,  243 
evacuation  of,  244 
Blastoderm,  355 
Blood,  136 

acid  in,  a  cause  of  death,  137 
calcium  phosphate  in,  38 
carbonates  in,  36 

changes  in,  due  to  respiration,  163 
circulation  of,  170 

effect  of  aspiration  of  thorax  on, 

188 
force  of  gravity  in,  188 
in  arteries,  183 
in  capillaries,  187 
internal  friction  in,  184 
in  veins,  187 
pressure  in,  185 
pulse- wave  in,  186 
coagulation  of,  143 
causes  of,  145 
influences  hastening,  145 
retarding,  145 


Blood,  color  of,  137 

compression  of,  in  veins,  188 

course  of  circulation  of,  175 

distribution  of,  137 

fibrin  in,  63 

fibrinogen  in,  63 

fluidity  of,  146 

gases  in,  147 

hEcmoglobin  in,  79 

hemorrhagic  diathesis,  147 

in  kidney,  oxygen  in,  148 

iron  in,  40 

microscopical  structure  of,  138 

movement  of,  during  systole   and 

diastole,  177 
odor  of,  137 
oxyhsemoglobin  in,  79 
physical  properties  of,  136 
quantity  of,  in  body,  137 
rate  of  flow  in  arteries,  185 
reactions  of,  137 
taste  of,  137 
temperature  of,  138 
Blood-clot,  cause  of,  63 

fibrin-ferment  in,  74 
Blood-corpuscles,  138 
number  of,  139 
red,  138 

color  of,  139 

destruction  of,  140 

development  of,  140 

functions  of,  140 

structure  of,  139 
white,  141 

composition  of,  142 

function  of,  142 
Blood-plasma,  143 
alkalinity  of,  34 
composition  of,  143 
Blood-plaques,  142 
Bones,  action  of   hydrochloric  acid 
on,  38 
"green-stick"  fracture  of,  38 
in  infancy,  calcium  phosphate  in, 

38 
in  old  age,  calcium  phosphate  in, 

38 
rigidity  of,  due  to  calcium  phos- 
phate, 38 

Boussingault's  experiments  in  sodium 
chloride,  33 

Brain,  246 


INDEX. 


369 


Brain,  basal  ganglia  of,  264 

centres  of  motion  of,  272 

control  of,  on  evacuation  of  blad- 
der, 244 

disease,   paralysis    of   pneuniogas- 
tric  after,  296 

gray  matter  of,  246 

lobes  of,  262 

weight  of,  246 

white  matter  of,  246 
Bread,  amount  of  proteids  in,  86 
Bronchi,  152 
Brunner's  glands,  120 
Burdach,  column  of,  232,  249 
Butter,  amount  of  fat  in,  85 
Butyric  acid,  normal,  54 

feiMuentation  of  dextrose,  49 

C. 

Calcium  carbonate  in  body,  39 
fluoride  in  body,  40 
phosphate,  37 

avenues  of  discharge  of,  39 
in  blood,  38 
in  foods,  39 
in  milk,  39 

quantity  of,  in  body,  37 
rigidity  of  bones  due  to,  38 
source  of,  38 
salts  in  body,  37 
Cane-sugar  (saccharose),  50 
Capillaries,  174 

circulation  of  blood  in,  187 
Capric  acid,  54 
Caproic  acid,  54 
Caprylic  acid,  54 
Carbohydrates,  41,  85 
Carbon  in  human  body,  26 

dioxide,  influence   of,  on    respira- 
tion, 162 
Carlxjnates  in  blood,  36 
in  ffxxls,  36 

in  fruits  and  vegetables,  36 
in  human  body,  36 
offices  of,  36 
Carljonic  acid  in  body,  41 
Carlxjn-monoxide  hx-moglobins,  79 
Cardiac  impulse,  180 
movements,  176 
sounds,  182 
causes  of,  182 

24 


Cardiac    sounds,    cliaractcristics    of, 
182 
valves,  172 
Casein  in  cow's  milk,  62 

differences  in,  in  human  and  cow's 

milk,  62 
in  human  milk,  61 
reactions  of,  62 
Cellular  or  vesicular  nervous  matter, 

217 
Cellulose,  47 

tests  for,  48 
Cerumen,  200 
Cerebellum,  256 

eft'ects  of  removal  of,  257 
functions  of,  257 
inferior  peduncles  of,  248 
structure  of,  256 
Cerebai  localization,  271 
Cer-ebrin,  76 

Cerebro-spinal  nervous  system,  227 
Cerebrum,  258 

auditory  centre  of,  274 

basal  ganglia  of,  264 

central  lobe  of,  263 

centre  for  speech,  273 

conscious  sensation  in,  271 

crura  cerebri,  263 

effect  of  destruction  of  tissues  of, 

269 
effect  of  removal  of   hemispheres 

of,  269 
fissures  of,  259 
Rolando's,  261 
Sylvius',  260 
frontal  lobe  of,  262 
functions  of,  268 

corpora  quadrigemina,  274 
corpora  striata,  274 
optic  thalami,  274 
great  longitudinal  fissure  of,  258 
hemispheres  of,  258 
lobes  of,  262 

localization  of  functions  of,  271 
microscopical    structure    of    gray 
matter  of,  265 
of  hemispheres,  265 
of  white  matter  of,  267 
motor  areas  of,  272 
occipital  lobe  of,  263 
olfactory  centre  of,  274 
optic  centre  of,  274 


370 


INDEX. 


Cerebrum,  optic  thalami  of,  264 
parietal  lobe  of,  263 
parieto-occipital  fissure,  261 
seat  of  intellectual  faculties,  269 
sensory  areas  of,  273 
temporo-sphenoidal  lobe  of,  263 
tubercula  or  corpora  quadrigemina, 
264 
Changes  in  circulation  at  birth,  365 
Cheese,  amount  of  fat  in,  85 
Chemical  changes  in  medulla  oblon- 
gata, 252 
elements  of  human  body,  25 
Chemistry  of  respiration,  159 
physiological,  25 
definii;ion  of,  25 
Cholesterin,  57 
Chondrin,  69 
Chorion,  360 
Choroid,  307 
Chyle,  132,  134 

composition  of,  134 
Chyme,  action  of  bile  on,  127 
formation  of,  in  stomach,  109 
in  intestinal  digestion,  127 
Ciliary  ganglion  of  trigeminus  nerve, 
288 
muscle  of  the  eye,  308 
Circulation,  changes  in,  at  birth,  365 
foetal,  362 
of  blood,  170 
course  of,  175 
friction  in,  184 
placental,  362 
vitelline,  362 
Clark's  vesicular  column,  335 

posterior  vesicular  column,  232 
Coagulation  of  blood,  143 
causes  of,  145 
influences  hastening,  145 
retarding,  145 
Cochlea,  326 
Collagen,  67 
Coloring-matters,  79 
Contractile  power  of  muscles  due  to 

water,  29 
Convulsion  in  asphyxia,  253 
Cornea,  307 

Corpora  striata,  ffinctions  of,  274 
quadrigemina,  264 
functions  of,  274 
Corpus  luteum,  formation  of,  35 1 


Corpuscles  of  Purkiuje,  257 
Corti,  organ  of,  327 
Cow's  milk,  casein  in,  62 
Cranial  nerves,  275 
Creatin,  210 
Creatinin,  212 
Crura  cerebri,  263 
Crystallin,  63 
Crystalline  lens,  311 
Cystitis,  influence  of,  on  evacuation 
of  bladder,  244 

D. 

Death,  acid  in  blood  as  a  cause  of,  35 
Defecation,  control  of  spinal   nerve- 
centres  on,  241 
involuntary,  242 
unconscious,  242 
Deglutition,  loi 

function  of  epiglottis  in,  102 
of  oesophagus  in,  102 
of  tongue  in,  loi 
influence  of  medulla  oblongata  on, 
249 
of  will  on,  loi 
stages  of,  101 
Depressor    nerve-fibres    of    medulla 

oblongata,  255 
Dextrose,  48 

alcoholic  fermentation  of,  48 
butyric  fermentation  of,  49 
lactic  fermentation  of,  49 
solubility  of,  48 
Diabetic  sugar,  48 

urine,  acetone  in,  53 
Diaphragm,  153 
Diastasic  enzyme  (ferment),  71 
Digestibility  of  food,  90,  112,  113 
Digestion,  92 

duration  of,  in  stomach,  112 
effect  of  alcohol  on,  115 
formation  of  chyme  in,  109 
functions  of  stomach  in,  103 

of  teeth  in,  97 
gases  in  stomach  during,  112 
gastric  juice  in,  106 
influence  of  emotions  on,  118 
intestinal,  118 

changes  of  sugar  in,  135 
chyme  in,  127 
emulsification  in,  127 


INDEX. 


Zl^ 


Digestion,    intestinal,    saponification 
in,  127 
mouth,  absorption  by,  in,  95 

function  of,  95 
muscular  movements   of  stomach 

in,  no 
normal   temperature    in    stomach 

during,   109 
pancreatic,  126 
pepsin  in  stomach,  I08 
rennin  in  gastric  juice  in,  108 
sodium  chlori<le  essential  to,  "^t, 
stomach-,  result  of.  III 
value  of  alcohol  in,  1 15 
Digestive  organs,  93 

piocess,diflusil)ility  of  foods  in,  95 
divisions  of,  94 
errors  in  knowledge  of,  94 
iion-difl'usibility  of  foods  in,  95 
rejection  of  extraneous  matters 

in,  94 
use  of  saliva  in,  98 
Diphtheria,  paralysis  of  pneumogas- 

tric  after,  296 
Drinking-water,  sulphates  in,  36 
Ductless  glands,  190 
Dysentery  due  to  impure  ice,  84 
Dyspepsia,  cause  of,  97 
Dyspnoea  in  asphyxia,  253 

E. 

Ear,  cochlea  of,  326 

Eustachian  tube  of,  33 1 

external,  323 

internal,  325 

labyrinth  of,  325 

middle,  324 

organ  of  Corti,  327 

semicircular  canals  of,  326,  331 

vestibule  of,  326 
"  Ear-wax,"  200 
Efferent  nerves,  223 
Egg-albumin,  59 
Egg-yolk,  vitellin  in,  63 
Eggs,  amount  of  fat  in,  85 
Elastin,  69 
Embryo,  circulation  in,  362 

membranes  of,  358 
allantois,  359 
amnion,  358 
chorion,  360 


Embryo,    membranes    of,    yolk-sac, 

359 

Emmetropia,  318 

Emulsification,  action  of  bile  in,  128 

in  intestinal  digestion,  127 

of  fat,  56 
End-bulbs  of  nerves,  221 
Enemata,  nutrient,  129 
Energy,  food  in  production  of,  92 
Enzymes,  70 

nomenclature  of,  71 
Epiblast,  355 

Epidermis,  structure  of,  196 
Epiglottis,  function  of,  in  deglutition, 

102 
Erythrodextrin,  conversion  of  starch 

into,  45 
Eskimos,  use  of  salt  by,  T^'i, 
Eustachian  tube,  331 
Ewald's  trial-meal  in  digestion,  114 
Exhaustion  in  asphyxia,  253 
Expiratory  movements,  155 

organs  concerned  in,  155 
External  ear,  323 
Eye,  accommodation  of,  3 1 5 

anterior  and  posterior  chambers  of, 
310 

appendages  of,  321 

arterial  supply  to,  312 

choroid  of,  307 

ciliary  muscle  of,  308 

cornea  of,  307 

crystalline  lens,  31 1 

defective  vision  in,  318 
ametropia,  318 
astigmatism,  319 
hypermetropia,  319 
myopia,  318 
presbyopia,  319 

elTect  of  paralysis  of  facial  nerve 
on,  291 

emmetropic,  318 

functions  of  retina,  319 

iris  of,  307 

lachrymal  ajjparatus  of,  321 

layers  of  retina,  309 

Meibomian  glands,  323 

retina  of,  309 

sclerotic  coat  of,  306 

suspensory  ligament  of,  312 

vitreous  body,  31 1 
Eyeball,  movements  of,  321 


372 


INDEX. 


Facial  nerve,  290 

effect  of  paralysis  of,  on  mouth, 
292 
on  taste,  292 
physiological  properties  of,  291 
paralysis,  291 

effect  of,  on  expression,  291 
on  eye,  291 
Faeces,  131 

amount  of  daily  evacuation,  131 
amount  of  water  discharged  in,  31 
indol  in,  78 
skatol  in,  78 
Fauces,  sense  of  taste  in,  303 
Fallopian  tubes,  343 
Fat,  aJDsorption  of,  135 
in  foods,  55 
offices  of,  55 
properties  of,  55 
saponification  of,  55 
source  of,  in  body,  54 
Fats,  53 
and  oils,  85 
food-stuffs,  83 
in  various  foods,  85 
emulsification  of,  56 
neutral,  54 
palmitin,  54 
stearin,  54 
olein,  54 
Fatty  acids,  53 
Female  genital  organs,  339 

respiration,  fallacy  of,  159 
Ferments,  70 

nomenclature  of,  71 
Fertilization  of  ovum,  354 
Fibrin-ferment,  74 

in  blood,  63 
Fibrinogen,  63 
in  blood,  63 
Fissure  of  Rolando,  262 

of  Sylvius,  260 
Foetal  circulation,  362 
Follicles  of  Lieberkiihn,  121 
Food,  82 

absorption  of,  92 
calcium  phosphate  in,  39 
cane-sugar  in,  50 
carbohydrates  in,  42 
carbonates  in,  36 


Food,  definition  of,  82 
digestion  of,  93 
digestibility  of,  90 
function  of  mouth  in  digestion  of, 

95 

gelatin  as  a  food,  68 

in  production  of  energy,  92 

in  supply  of  waste,  92 

maintenance  of  body  by,  87 

mastication  of,  96 

nitrogenous,  effects  of  excess  of,  88 

quantity  of  sodium  chloride  in,  t,}, 
of  starch  in,  44 
of  water  in,  30 

starch  in,  42,  44 

use  of  salt  in,  84 

variation  in,  essential  to  health,  87 
Foods,  amount  of  food-stuffs  in  vari- 
ous, 86 

digestibility  of  various,  112,  113 

effects  of,  on  urine,  208 

fat  in,  55 

fattening,  55 

formation  of  urea    from   proteids, 
210 

mixture  of,  value  of  a,  88 

nitrogenous,  85 

variety  of,  efficiency  of  a,  88 
Food-stufl's,  divisions  of,  83 
Formation  of  corpus  luteum,  351 
Formic  acid,  53 
Fovea  centralis  of  retina,  320 
Fruits  and  vegetables,  carbonates  in, 

36 
Funiculus   cuneatus   of   medulla  ob- 
longata, 249 

gracilis  of  medulla  oblongata,  24S 

Rolando  of  medulla  oblongata,  248 
Fuscin,  81 


Galactose,  50 
Ganglia,  intrinsic,  254 

of  trigeminus  nerve,  288 
Gases  in  blood,  147 

in  stomach  during  digestion,  1 12 
Gastric  juice  and  saliva,  composition 
of,  107 
artificial,  114 

free  hydrochloric  acid  in,  108 
influence  of  emotions  on,  118 


INDEX. 


373 


Gastric  juice,   in    stomach-digestion, 
1 06 
quantity  of,  in  stomach,  106 
rennin  in,  108 
Gelatin,  67 
as  a  food,  68 
composition  of,  68 
reactions  of,  68 
solubility  of,  68 
General  sensibility,  299 
Genital  organs  of  female,  339 

of  male,  336 
Gerlach's  nerve-network,  232 
Germicide  action  of  juices  of  stom- 
ach, 1 17 
Gland,  pineal,  194 
thymus,    193 
thyroid,  194 
Glands,  ductless,  191 

lymphatic,    190 
Globin,  64 
Globulins,  63 

sodium  chloride  as  a  solvent  of,  32 
Glomerulus,  effects  of  blood-pressure 

in,  209 
Glosso-pharyngeal  nerve,  293 

physiological  properties  of,  293 
Glottis,  movements  of,  in  respiration, 

156 
Glucose,  48 
Glycogen,  46,  136 
reactions  of,  47 
Gmelin's  test  for  biliverdin,  80 
GoU,  column  of,  231,  249 
Graafian  vesicles,  340 
Grains,  amount  of  proteids  in,  86 
Grape-sugar,  48 
Gravity,   force    of,   in   circulation   of 

blood,  188 
(jray  matter  of  brain,  structure   of, 
267 
nervous  matter,  217 
Gustatory  nerve,  285 

H. 

HjEmatin,  79 
Ifaemin-crystals,  79 
Haemoglobin,  79 

carlxjn  montjxiiie  in,  79 

C<)miK)silion  of,  79 
Hx-morrhagic  diathesis,  147 


Hairs  and  nails,  200 

number  of,  in  head,  200 
Headache    due   to   affections  of   tri- 
geminus nerv'e,  284 
Hearing,  mechanism  of,  328 
sense  of,  323 

telephone  theory  of  sense  of,  330 
Heart,  170 

aortic  valve  of,  174 
"apex-beat"  of,  180 
auricular  diastole  of,  177 

systole  of,  176 
left  auricle  of,  171 
ventricle  of,  171 
mitral  valve  of,  173 
movements  of,  176 
papillary  muscles  of,  180 
pulmonary  valve  of,  173 
right  auricle  of,  170 

ventricle  of,  170 
shortening  of,  during  systole,  180 
cardiac  valve  of,  172 
tricuspid  valve  of,  172 
ventricular  diastole  of,  177 
systole  of,  177 
Heart-sounds,  182 
characteristics  of,  182 
causes  of,  182 
Heat,  movement  a  cause  of,  167 
oxidation  a  cause  of,  167 
sources  of,  1 66 
vital,  164 
Heal-unit,  166 

Helmholtz,  phakoscope  of,  317 
Hemispheres,  microscopical  structure 

of,  265 
Hippuric  acid,  78 
in  urine,  212 
Homoiothermal  animals,  165 
Human  body,  carbon  in,  26 

chemical  elements  of,  25 
Humidity,   influence  of,  on   respira- 
tion, 160 
Hydrobilirubin,  81 
Hydrochloric  acid  in  body,  41 

in  gastric  juice,  108 
Hydrogen  in  liody,  41 

sulphuretted,  in  body,  41 
Hydrolytic  enzyme  (ferment),  72 
Hypermetropia,  319 
Hyperjiyrexia  due  to  injury  of  pons 
Varolii,  256 


374 

Hypoblast,  355 
Hypoglossal  nerve,  298 

I. 

Ice,  impure,  danger  of  use  of,  83 

dysentery  due  to,  84 
Impulses,  spinal  cord  as  a  conductor 

of,  235 
Indigestion,  cause  of,  97 
Indol,  78 

Inferior    maxillary    division    of    tri- 
geminus, 283 
Inorganic  food-stuffs,  83 

physiological  ingredients,  27 
Inosit  (muscle-sugar),  50 
Insalivation,  98 
Inspiratory  movements,  154 
organs  concerned  in,  154 
spasm  in  asphyxia,  253 
Internal  ear,  325 
respiration,  163 
Intestinal  digestion,  1 18 
bile  in,  123 

change  of  sugar  in,  135 
chyme  in,  127 
emulsification  in,  127 
saponification  in,  127 
juice,  121 

action  of,  on  food,  121 
villi,  structure  of,  132 
Intestine,  large,  129 

absorptive  powers  of,  129 
faeces  in,  131 
small,  Brunner's  glands  in,  120 
coats  of,  118 
villi  of,  119 
Iris,  307 

Iron,  avenues  of  discharge  of,  41 
in  blood,  40 
in  body,  40 
source  of,  40 
office  of,  40 
Island  of  Reil,  263 
Isobutyric  acid,  54 

J- 

Jackson  on  menstruation,  350 
Judgment,  270 


INDEX. 


K. 


Keratin,  69 


Kidneys,  204 

amount  of  water  discharged  from, 

31 

anatomy  of,  205 
capsule  of  Bowman,  206 
cortex  of,  205 
formation  of  urine  in,  207 
Malpighian  capsule  of,  207 

pyramids  of,  206 
medulla  of,  205 
oxygen  in  blood  of,  148 
reciprocal  relations  of,  with    skin, 

201 
renal  artery,  207 
vein,  207 
Kreatin,  76 
Kreatinin,  76 

L. 

Labyrinth  of  ear,  325 
Lachrymal  apparatus,  321 
Lactic  acid,  56 

fermentation  of  dextrose,  49 
Lactose,  52 

fermentation  of,  53 

solubility  of,  52 
Lsevulose,  49 
Large  intestine,  129 
Laryngeal  plexus,  295 
Lecithin,  76 
Leucin,  78 

Lieberkiihn,  follicles  of,  121 
Lingual  nerve,  285 
Liver,  glycogen  in,  47 

secretion  of  bile  in,  123 
Lobes  of  cerebrum,  262 
Lungs,  152 

capacity  of,  157 

amount  of  water  discharged  from, 

31 

density  of  air  in,  157 

pneumogastric  nerve  of,  295 
Lutein,  82 
Lymph,  133 

composition  of,  134 
Lymphatic  glands,  190 
functions  of,  191 

system,  189 

vessels,  189 

M. 

Macula  lutea  of  retina,  320 


INDEX. 


375 


Magnesium  carbonate  in  l)o<ly,  40 
phosphate  in  body,  40 
salts  in  body,  40 
Male  genital  organs,  336 
Malpighian  capsule,  207 
Malto-dextrin,  conversion    of  starch 

into,  46 
Maltose,  51 
reactions  of,  52 
solubility  of,  52 
Marsh-gas,  in  body,  41 
Mastication,    control    of    trigeminus 
nerve  on,  2S5 
imperfect,  a  cause  of  dyspepsia,  97 
of  food,  96 
Maturation  of  ovum,  351 
Meat,  amount  of  fat  in,  85 
of  ])roteids  in,  86 
diet,  eft'ect  of  exclusive,  88 
Mechanism  of  hearing,  328 
Meckel's  ganglion  of  trigeminus,  288 
Medulla  oblongata,  247 

automatic  centres  of,  250 
cardio-inhibitory  centre  of,  254 
chemical  changes  in,  252 
composition  of,  247 
dejiressor  nerve-fibres  of,  255 
fissure  of,  248 
functions  of,  249 
funiculi  of,  248 

influence  of,  on  central  vomiting, 
250 
on  deglutition,  249 
on  respiratory  centre,  251 
on  rumination,  250 
on  vomiting,  249 
nerve-centres  of,  249 
posterior  columns  of,  247 
rellex  centres  of,  249 
respiratory  centre  of,  251 
restiform  Ijodics  of,  248 
vasomotor  centre  of,  254 
Meibomian  glantls,  323 
Mclanins,  81 
Mcmbrana  jiropria,  340 
Memory,  270 

Menses,  composition  of,  34S 
Mcnsti nation,  347 

and    ovulation,   relation    between, 

cause  of,  349 

change  in  uterus  during,  348 


Menstruation,  ovular  theory  of,  350 

Mesoblast,  355 

Micturition,  control  of  nerve-centres 

on,  243 
Middle  ear,  324 
Milk,  amount  of  fat  in,  85 
of  proteids  in,  86 
calcium  phosphate  in,  39 
cow's,  casein  in,  62 
human,  casein  in,  61 
lactose  in,  52 
Milk-sugar,  52 

Motion,  centre  of,  m  brain,  273 
Motor  nerves,  224 
Motor-oculi  nerve,  278 
paralysis  of,  279 
result  of  paralysis  of,  279 
external  strabismus,  279 
inability  to  focus,  280 
luscitas,  280 
mydriasis,  280 
ptosis,  280 
Mouth,  absorption  by,  in  digestion,  95 
effect  of  paralysis  of  facial    nerve 

on,  292 
function  of,  in  digestion,  95 
Mouth-breathing,  evil  effects  of,  150 
Movement  as  a  cause  of  heat,  167 
Mucin,  66 
in  bile,  67 
reactions  of,  67 
Muscular  movements  of  stomach,  1 10 
"  Muscular  tone,"  cause  of,  254 
Muscle-enzyme  (ferment),  74 
Muscles,  contractile  power  of,  due  to 
water,  29 
water  in,  29 
Myopia,  318 
Myosin,  63 

N. 

Nails  and  hairs,  200 
Nerve,  abducens,  289 
]iaralysis  of,  290 

auditory,  292 

facial,  290 

glosso  jiltaryngcal,  293 

physiological  properties  of,  293 

gustatory,  285 

liy|)oglossal,  298 

lingual,  285 


3/6 


INDEX. 


Nerve,  motor-oculi,  278 
olfactory,  276 

function  of,  277 
optic,  277 

function  of,  278 
insensitiveness  of,  to  light,  320 
pneumogastric,  293 
spinal  accessory,  297 
trigeminus,  281 
trochlearis,  281 
Nerve-cells,  217 

and  nerve-fibres,  functions  of,  221 
Nerve-centres,  217 
automatic,  222 
classification  of,  221 
conscious,  222 

influence  of,  on  evacuation  of  blad- 
der, 244 
junction,  222 
reffex,  222 
reflex  action  of,  238 
relay,  222 

spinal  cord  as  a,  237 
Nerve-fibres,  classification  of,  222 
of  gray  matter  of  spinal  cord,  232 
termination  of,  220 
Nerve-stimuli,  226 
classification  of,  227 
general,  227 
special,  227 
Nerves,  afferent,  224 
inhibitory,  225 
cranial,  275 
degeneration  of,  236 
efferent,  223 

inhibitory,  224 
excito-reflex,  225 
extrinsic,  254 
intracentral,  225 
motor,  224 
of  special  sense,  225 
secretory,  224 
sensory,   225 
spinal,  233 

divisions  of,  233 
functions  of,  233 
recurrent  sensibility  of,  233 
stimulation  of,  233 
thermic,  225 
trophic,  224 
vaso-motor,  224 
Nervous  functions,  215 


Nervous  impulses,  rate  of  travel,  227 
matter,  cellular  or  vesicular,  217 

chemistry  of,  221 

cineritious,  217 

corpuscles  of  Pacini,  221 

end-bulbs,  221 

fibrous,  219 

gray,  217 

medullated  fibrous,  219 

non-medullated  fibrous,  220 

Remak,  fibres  of,  220 

Schwann,  substance  of,  219 

tactile  corpuscles,  221 
system,  action  of  alcohol  on,  116 

cerebro-spinal,  227 

general  arrangement  of,  227 

sympathetic,  331 
Neuralgia  due  to  affections  of  the  tri- 
geminus nerve,  284 
Nitrogen  in  body,  41 
Nitrogenous  foods,  85 

effects  of  excess  of,  88 
Nomenclature  of  ferments,  71 
Nose,  office  of,  in  respiration,  149 
Nutrient  enemata,  129 
Nutritive  functions,  92 

O. 

Oesophageal  plexus,  295 
Oesophagus,  function  of,  in  degluti- 
tion, 102 
Olfactory  centre  of  brain,  274 
nerve,  276 

function  of,  277 
Ophthalmic    division    of    trigeminus 

nerve,  282 
Optic  centre  of  brain,  274 
nerve,  277 

function  of,  278 
insensitiveness  of,  to  light,  320 
thalami,  functions  of,  274 
Osmosis,  sodium  chloride  in,  32 
Ossein,  67 

Ovarian  pregnancy,  353 
Ovaries,  339 

weight  of,  340 
Ovary,  life  of  human,  346 
Ovular  theory  of  menstruation,  350 
Ovulation,  345 

and     menstruation,     relation     be- 
tween, 350 


INDEX. 


377 


Ovulation,  theories  of,  346 
Ovum,  342 

fertilization  of,  354 

maturation  of,  351 
Oxidation  as  a  cause  of  heat,  167 
Oxygen  in  blood  of  kidney,  148 

in  l:)ody,  41 

in  internal  respiration,  164 

in  respiration,  149 
Oxyhemoglobin,  79 

P. 

Pacini,  corpuscles  of,  221 
I'ain,  sense  of,  300 
Pancreatic  iligestion,  126 
ferments,  125 
amylopsin,  125 
steapsin,  125 
trypsin,  126 
juice,  124 

action  on  starch,  45 
amylopsin  in,  45 
composition  of,  125 
Papillary  muscles  of  heart,  iSo 
I'araglobulin,  63 

Paralysis  due  to  injury  of  pons  Varo- 
lii, 256 
of  facial  nerve,  effect  of,  on    eye, 
291 
on  expression,  291 
on  mouth,  292 
on  taste,  292 
Parovarium,  342 
Peas  and  beans,  amount  of  jnoteids 

in,  86 
Pepsin,  72 

action  of,  on  proteids,  64 
in  stomach-digestion,  108 
Pe])toncs,  66 
reaction  of,  66 
solubility  of,  66 
Perspiration,    amount    formed    daily, 
198 
comjiosition  of,  19S 
office  of,  199 

influence  of,  on  temperature,  199 
"  insensible,"  I9.S 
Perspiratory  glands,  196 

of  skin,  196 
I'ettenkofer's  test  for  bilcacids,  75 
Payer's  patches,  121 


Phakoscope  of  Ilelmholtz,  317 
Pharyngeal  plexus,  295 
Pharynx,  sense  of  taste  in,  303 
Phosphates,  alkaline,  34 

avenues  of  discharge  of,  35 
office  of,  34 
source  of,  35 
Phrenic  nerves,  connection  of,  with 

life,  249 
Pialyn,  74 

action  of,  on  neutral  fats,  74 
Pineal  gland,  194 
Pituitary  liody,  194 
Placenta,  360 
Placental  circulation,  362 
Pneumogastric  nerve,  293 

cardiac  branches  of,  296 
Poikilothermal  animals,  165 
Pons  Varolii,  255 

effects  of  division  of,  256 
of  stimulation  of,  256 
functions  of,  256 
hyperpyrexia    caused    by   injury 

to,   256 
lesions  of,  256 

paralysis  causeil  liy  injury  to,  256 
structure  of,  255 
Potassium  chloride,  avenues  of   dis- 
charge of,  37 
in  body,  37 
source  of,  37 
phosphate  in  human  body,  34 
sulpiiate  in  human  body,  35 
P(jtatoes,  amount  of  jiroteids  in,  86 
Pregnancy,  alxlominal,  353 

ovarian,  353 
Presbyopia,  319 
Pressure,  sense  of,  300 
Proprionic  acid,  54 
Protagon,  76 
Pr<jteids,  57,  85 

action  of  pepsin  on,  64 

of  trv|isin  on,  64 
classification  of,  58 
composition  of,  57 
food-stuffs,  83 
of  blood  and  lymph,  formation  of 

urea  from,  210 
of  f<K)d,   formation   of    urea   froni. 

210 
of  tissue,  formation   r)f  urea  from, 
210 


378 


INDEX. 


Proteids,  reactions  of,  57 
Millon's,  58 
Piotrowski's,  58 
xanthoproteic,  58 
value  of,  as  food,  85 
Proteolytic  enzyme  (ferment),  72 
Pulmonary  plexus,  295 
Pulse- wave   in    circulation   of  blood, 

186 
Ptyalin,  72 
in  saliva,  45 

Q 

Quantity  of  water  in  the  human  body, 
28 

R. 

Reason,   270 

Recurrent  sensibility,  233 

sensory  fibres  of  spinal  nerves,  234 
Reflex  action,  237 

afferent  nerves  in  23S 

during  sleep,  239 

effect  of  drugs  on,  240 

efferent  nerves  in,  238 

not  spontaneous,  238 

of     vesico-spinal     nerve-centre, 

244 
stimuli  in,  238 
Reil,  island  of,  263 
Relation  between  ovulation  and  men- 
struation, 350 
Relationship  between  different  parts 

of  body,  214 
Remak,  fibres  of,  220 
Renal  artery,  207 

veins,  207 
Rennin,  74 

in  gastric  juice,  108 
Reproductive  functions,  336 
Resistance  theory  of  respiration,  251 
Respiration,  149 
abdominal,  158 
capacity  of  lungs  in,  157 
carbon  dioxide  in,  162 
cause  of,  158 
cause    of    rhythmic    cliaracter    of, 

252^ 
changes  in  lilood  due  to,  163 
chemistry  of,  159 


Respiration,  costal,  158 

expired  air  in,  composition  of,  160 

"female,"  fallacy  of,  159 

frequency  of,  158 

influence  of  humidity  on,  160 

internal,  163 
oxygen  in,  164 

movements  of  glottis  in,  156 

nose  in,  149 

oxygen  in,  149 

resistance  theory  of,  251 

through  skin,  203 
.types  of,  158 

vital  capacity  in,  158 
Respiratory  centre  of  medulla  oblon- 
gata, 251 

movements,  154 

organs,  149 
Retina,  309 

fovea  centralis  of,  320 

functions  of,  319 

layers  of,  309 

macula  lutea  of,  320 

theory  of  chemical  changes  in,  320 
Rhythmic    character    of    respiration, 

cause  of,  252 
Riegel's  trial-meal  in  digestion,  1 14 
Rigor  mortis,  cause  of,  63 
Rolando,  fissure  of,  261 
Rumination,    influence    of    medulla 

oblongata  on,  251 
Rutherford  on   telephone    theory  of 
hearing,  330 

S. 

Saccharose  (cane-sugar),  50 

in  food,  50 
Saliva,  99 

action  of,  on  starch,  45 

and  gastric  juice,  composition  of, 
107 

chemical  action  of,  99 

influence  of,  on  sense  of  taste,  100 

mechanical  action  of,  100 

office  of,  99 

ptyalin  in,  45,  72 

use  of,  in  digestive  process,  98 
Salivary  calculi,  formation  of,  99 

glands,  98 
Salts  as  inorganic  foods,  84 

in  human  body,  offices  of,  32 


INDEX. 


379 


Saponification  in  intestinal  digestion, 
127 
of  fat,  55 
Sarcolactic  acid,  57 
Schneiderian  membrane  in  sense  of 

smell,  301 
Schwann,  substance  of,  219 
Sclerotic  coat  of  eye,  306 
Sebaceous  glands,  199 
Sebum,  199 

composition  of,  200 
Seminal  cells,  336 
Seminiferous  tubules,  338 
Sensation,   conscious,    in    cerebrum, 

271 
Senses,  299 
Sense  (jf  hearing,  323 
of  pain,  300 
of  pressure,  300 
of  sight,  306 
of  smell,  301 

aculeness  of,  303 
functions  of  Schneiderian  mem- 
brane in,  301,  302 
of  taste,  303 

conditions  of,  305 
in  fauces,  303 
in  pharynx,  303 
in  soft  palate,  303 
in  tonsils,  303 
in  uvula,  303 
means  of  excitation,  306 
temperature,  300 
touch,  299 
Sensibility,  general,  299 

tactile,  300 
Sensory  areas  of  brain,  273 

impulse,  course  of,  in  spinal  cord, 

237 
Serum-albumin,  59 
Serum-lutein,  82 
Shock,  reflex  action  diminished   by, 

240 
Sight,  sense  of,  306 
Silicon  in  iKxly,  41 
Skatol,  78 

Skene  on  menstruation,  347 
Skin,  195 

amount  of  water  discharged  from, 

31 
care  of,  203 
baths  in,  203 


Skin,  care  of,  friction  in,  203 
soap,  use  of,  in,  203 
corium  of,  195 

effect  of  water  on  functions  of,  30 
epidermis  of,  196 
excretions  through,  201 
formation  of  sebum  in,  200 
functions  of,  200 
perspiratory  glands  of,  196 
functions  of,  197 
number  of,  196 
protection  of  tissues  by,  201 
reciprocal  relations  with  kidneys, 

201 
respiration  through,  203 
sebaceous  glands  of,  199 
sensation  in,  202 
temperature,  influence  on,  203 
Sleep,  reflex  action  during,  239 
Smell,  sense  of,  301 
Sodium  bicarbonate  in  body,  36 
chloride,  avenues  of  discharge  from 
body,  34 
Boussingault's    exjierinients    in, 

essential  to  digestion,  t^t, 

offices  of,  32 

quantity  of,  in  food,  33 

in  human  body,  32 
source  of,  32 
use  of,  by  Eskimos,  I,'}, 
glycocholate,  75 
phosphate  in  human  body,  34 
suljihate  in  human  body,  35 
taurocholate,  75 
Soft  palate,  sense  of  taste  in,  303 
Soluble  starch,  45 
Solubility  of  starch,  44 
Sources  of  water  in  human  body,  30 
Sjiecial  senses,  connection  nf  trigem- 
inus nerve  with,  2S6 
Speech,  centre  of,  in  brain,  273 
Spermatoblasts,  338 
Spermatozoa,  336 
motion  of,  339 
Spleen,  r92 

congenital  al)sence  of,  193 
functions  of,  192 
Sjjinal  accessory  nerve,  297 
cord,  228 

ano-s]iinal  centre  of,  241 
anterior  or  jnotor  roots  of,  234 


38o 


INDEX. 


Spinal  cord,  as  a  conductor  of   im- 
pulses, 235 
as  a  nerve-centre,  237 
cardio-accelerator  centre  of,  241 
cilio-spinal  centre  of,  241 
conducting  paths  in,  236 
connection  of  nerve-roots  with, 

234 
control  of,  on  defecation,  242 
course  of   sensory  impulses  in, 

237 

degeneration  of,  236 
in  fibres  of,  236 

effect  of  drugs  on  reflex  action 
of,  240 

efferent  impulses  in,  independent 
of  will,  239 

enlargements  of,  228 

fissures  of,  228 

genito-spinal  centre  of,  241 

gray  matter  of,  232 

nerve-cells  in,  232 
nerve-fibres  of,  232 

methods  of  examination,  235 
degenerative,  236 

minute  structure  of,  230 

niusculo-tonic  centre  of,  240 

posterior  or  sensory  root  of,  235 

reflex  action  in,  238 

respiratory  centre  of,  240 

section  of,  230 

special  centres  of,  240 

sudorific  centre  of,  241 

tracts  in,  230 

anterior  radicular  zone,  231 
cerebellar  column,  231 
cohmin  of  Burdach,  231 

of  Goll,  231 
crossed  pyramidal   fasciculus, 

231 
fasciculus  of  Tiirck,  231 
fundamental  fasciculus,  231 
mixed  lateral  column,  231 

trophic  nerve-centres  of,  245 

various  centres  of,  245 

vaso-motor  centre  of,  241 

vesicospinal  centre  of,  243 
ganglia,  functions  of,  234 
nerves,  233 

division  of,  233 

functions  of,  233 

recurrent  sensibility  of,  233 


Spinal  nerves,  stimulation  of,  233 
Starch,  42 

action  of  pancreatic  juice  on,  45 

adulterations  of,  44 

conversion  of,  into  achroodextrin, 
46 
into  erythrodextrin,  45 
into  maltodextrin,  46 

effect  of  saliva  on,  45 

in  various  foods,  42,  44 

quantity  of,  in  food,  44 

solubility  of,  44 

tests  for,  44 
Starvation,  time  necessary  to  produce, 

82 
Steapsin,  125 

Stilling's  sacral  nucleus,  335 
Stomach,  action  of  alcohol  on,  117 

cells  of,  104 

coats  of,  103 

digestion  in,  103 

duration  of  digestion  in,  112 

gases  in,  during  digestion,  112 

gastric  juice,  quantity  of,  in,  106 

germicide  action  of  juices  of,  117 

glands  of,  104 

muscular  movements  of,  in  diges- 
tion, no 

of  Alexis  St.  Martin,  106 

peristaltic  movements  in,  I  lO 

pneumogastric  nerve  of,  295 

self-digestion  of,  in 

vascularity  of,  105 

vermicular  movement  in,  no 
Stomach-digestion,  results  of,  in 
Submaxillary  ganglion  of  trigeminus 

nerve,  289 
Sugar,  48 

changes  in,  in  intestinal  digestion, 

of  milk,  52 
Sulphates  in  drinking-water,  36 

in  human  body,  35 

sources  of,  in  human  body,  35 
Sulphuretted  hydrogen  in  body,  41 
Superior    maxillary    division    of   tri- 
geminus nerve,  282 
Suprarenal  capsules,  194 
Suspensory  ligament  of  eye,  312 
Sutton's  theories  of  ovulation,  346 
Swallowing,  act  of,  loi 
Sweat,  198 


INDEX. 


381 


Semicircular  canals  of  ear  326,  331 
Sylvius,  tissure  of,  260 
Sympathetic  ganglia  and  nerves,  t,},^^ 
nervous  system,  331 
functions  of,  334 
Syntonin,  60 

T. 

Tactile  corpuscles,  22 1 

sensibility,  300 
Tait's  theories  of  ovulation,  346 
Tartar,  formation  of,  99 
Taste,  effect    of    paralysis    of   facial 
nerve  on,  292 

influence  of  saliva  on  sense  of,  100 

sense  of,  303 
Teeth,  96 

function  of,  in  tligesliun,  97 

imperfect,  a  cause  of  indigestion,  97 
Telephone  theory  of  sense  of  hearing, 

330 
Testes,  336 
Temperature  at  different  ages,  167 

influence  of  alcohol  on,  116 

influence  of  skin  on,  203 

instances  of  high,  168 
of  low,  168 

normal,  in  stomach-digestion,  109 

of  blood,  138 

of  various  parts  of  the  body,  167 

regulation  of,  169 

of,  by  perspiration,  199 

sense  of,  300 

variations  of,  168 
Thorax,  153 

aspirati(jn  of,  effect  on  circulaliun 
of  blood,  188 
'Ihymus  gland,  193 
Thyroid  gland,  194 
Tissues,  formation  of  urea  from  pro- 

teids  of,  210 
Tongue,  circumvallale  paiiilhx'  of,  304 

tdiform  pa|)illa;  of,  305 

function  (;f,  in  deglutition,  loi 

fungiform  papilliv  of,  305 

sensitive  portions  of,  303 
Tonsils,  sense  of  taste  in,  303 
Toothache  due  to   affections  of   tri- 
geminus nerve,  284 
Touch,  sense  of,  299 
Trachea,  151 


Trigeminus  nerve,  281 

connection      of,    with      special 

senses,  286 
control  of  mastication  in,  285 
divisions  of,  282 
ganglia  of,  288 
ciliary,  288 
otic  or  Arnold's,  289 
spheno-palatine   or  Meckel's, 

288 
submaxillary,  289 
headache    due  to  affections  of, 

284 
inferior  maxillary  division  of,  283 
lingual  branch  of,  285 
neuralgia  due  to  affections  of,  284 
physiological  properties  of,  283 
toothache  due   to   affections  of, 
284 
Trochlearis  nerve,  281 
Trypsin,  73 

action  of,  in  intestinal  digestion,  126 
on  jiroteids,  64 
Tuber  annulare  (or  mesocephalon), 

25s 
Tunica  albuginea,  340 
fibrosa,  341 
vasculosa,  341 
Turck,  fasciculus  of,  231 
Tympanum,  324 
Typhoid  fever  due  to  impure  water, 

84 
Tyrosin,  78 

U. 

Urea,  77,  209 
source  of,  209 

from    prc)teids    of     blood    and 

lymiih,  260 
from  proteids  of  food,  209 
from  proteids  of  tissues,  210 
Uric  acid,  77,  211 
source  of,  212 
Urinary  melanin,  81 
Urine,  coloring-matter  of,  214 
com])osition  of,  208 
control  of  nerve-centres  on  passage 

of,  243 
creatinin  in,  212 
diabetic  acetone  in,  53 
effects  of  foods  on,  208 


382 


INDEX. 


Urine,  formation  of,  207 

gases  in,  214 

hippuric  acid  in,  78,  212 

hydrobilirubin  in,  81 

inorganic  constituents  of,  212 

melanin  in,  81 

mucus  in,  214 

quantity  voided  daily,  208 

specific  gravity  of,  207 

urea  in,  77,  209 

uric  acid  in,  77,  211 

urochrome  in,  81 

variations  of,  in  health,  208 
Urochrome,  81 
Uterus,  345 

change    in,  during     menstruation, 
348 
Uvula,  sense  of  taste  in,  303 


Valvulse  conniventes,  119 

Variety  of  foods,  efficiency  of  a,  88 

Vascular    system,  action    of   alcohol 

on,  116 
Vas  deferens,  339 
Vegetable  foods,  starch  in,  42,  44 
Vegetables  and  fruits,  carbonates  in 

Vegetarianism,  89 

atheromatous  degeneration  due  to, 
89 

cause  of  phosphaturia,  90 
of  senile  arch  of  cornea,  90 
of  tartar,  90 

fallacy  of,  89 
Veins,  175 

circulation  of  blood  in,  187 

compression  of  blood  in,  188 

valves  in,  175 
Ventilation,  161 
Ventricles  of  heart,  170 
Ventricular  diastole,  177 

systole,  177 
Vernix  caseosa,  200 
Vesicula  seminalis,  339 
Vesico-spinal  nerve-centre,  reflex  ac- 
tion of,  244 
Vestibule  of  ear,  326 


Villi  of  small  intestine,  1 19 
Vision,  physiology  of,  312 
Visual  centre  of  brain,  274 
Vital  capacity  in  respiration,  158 

heat,  164 
Vitellin,  63 

Vitelline  circulation,  362 
Vitreous  body,  31 1 
Vomiting,  influence  of  medulla  ob- 
longata on,  249 

W. 

Waldeyer's  germinal  epithelium,  340 
Warm-blooded  animals,  165 
Waste,  food  in  supply  of,  92 

of  body,  daily  amount  of,  87 

of  human  body,  82 

products  of  body,  76 
Water,  28 

amount  discharged  in  fceces,  31 
from  kidneys,  31 
from  lungs,  31 
from  skin,  31 

amount  excreted  daily,  209 

as  a  food,  83 

as  a  physiological  ingredient,  26 

as  a  solvent  of  food,  83 

avenues  of  elimination  from  body, 

effect  of,  on  functions  of  skin,  30 

impure,  danger  of  use  of,  83 
typhoid  fever  due  to,  84 

in  food,  quantity  of,  30 

in  body,  offices  of,  29 

in  muscles,  29 

quantity  of,  in  human  body,  28 

sources  of,  in  human  body,  30 
White  matter  of  brain,  structure  of, 

267 
Will,  influence  of,  on  deglutition,  loi 


Yolk-sac,  359 


Zymogen,  71 


JUN  2  6    mS 


